Collision avoidance between epdcch and aperiodic csi-rs

ABSTRACT

Methods, wireless devices and network nodes for avoiding collision between a downlink control channel and a aperiodic channel state information reference signal, aperiodic CSI-RS, are provided. According to some aspects, a method is provided that includes receiving an aperiodic channel state information reference signal, aperiodic CSI-RS, based on an assumption that the aperiodic CSI-RS is not present in physical layer resources corresponding to a downlink control channel set.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority to U.S. patentapplication Ser. No. 15/578,365, filed on Nov. 30, 2017, entitledCOLLISION AVOIDANCE BETWEEN EPDCCH AND APERIODIC CSI-RS, which claimspriority to PCT Application No. PCT/IB2017/056554, filed on Oct. 20,2017, entitled COLLISION AVOIDANCE BETWEEN DOWNLINK CONTROL CHANNELS ANDAPERIODIC CHANNEL STATE INFORMATION-REFERENCE SIGNALS, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/411,413,filed on Oct. 21, 2016, entitled COLLISION AVOIDANCE BETWEEN EPDCCH ANDAPERIODIC CSI-RS, and to U.S. Provisional Patent Application Ser. No.62/418,009, filed Nov. 4, 2016, entitled COLLISION AVOIDANCE BETWEENEPDCCH AND APERIODIC CSI-RS, the entireties of all of which areincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to methods, network nodes, wireless devices,computer programs and computer program products thereof for configuringaperiodic channel state information reference signals (CSI-RS and, inparticular, for avoiding collision between downlink control channel andaperiodic channel state information reference signals (CSI-RS).

BACKGROUND

Long-Term Evolution (LTE) uses Orthogonal Frequency DivisionMultiplexing (OFDM) in the downlink and Discrete Fourier Transform(DFT)-spread OFDM in the uplink. The basic LTE downlink physicalresource can thus be seen as a time-frequency grid as illustrated inFIG. 1, where each resource element corresponds to one OFDM subcarrierduring one OFDM symbol interval. [3GPP TS 36.211 Technical SpecificationGroup Radio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Physical channels and modulation (Release 13); V13.0.0(2016-01)].

In the time domain, LTE downlink transmissions are organized into radioframes of 10 ms, each radio frame consisting of ten equally-sizedsubframes of length T_(subframe)=1 ms as shown in FIG. 2.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. Resource blocks are numbered in the frequency domain,starting with 0 from one end of the system bandwidth.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe base station transmits control information indicating to whichterminals data is transmitted and upon which resource blocks the data istransmitted, in the current downlink subframe. This control signallingis typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in eachsubframe. A downlink system with 3 OFDM symbols used for control isillustrated in FIG. 3.

Physical Channels and Transmission Modes

In LTE, a number of physical downlink (DL) channels are supported. Adownlink physical channel corresponds to a set of resource elementscarrying information originating from higher layers. The following aresome of the physical channels supported in LTE:

-   -   Physical Downlink Shared Channel, PDSCH    -   Physical Downlink Control Channel, PDCCH    -   Enhanced Physical Downlink Control Channel, EPDCCH        The PDSCH is used mainly for carrying user traffic data and        higher layer messages. The PDSCH is transmitted in a DL subframe        outside of the control region as shown in FIG. 3. Both the PDCCH        and the EPDCCH are used to carry Downlink Control        Information (DCI) such as Physical Resource Block (PRB)        allocation, modulation level and coding scheme (MCS), precoder        used at the transmitter, and etc. The PDCCH is transmitted in        the first one to four OFDM symbols in a DL subframe, i.e. the        control region, while the EPDCCH is transmitted in the same        region as the PDSCH.

Similarly, the following physical UL channels are supported:

-   -   Physical Uplink Shared Channel, PUSCH    -   Physical Uplink Control Channel, PUCCH        Different DCI formats are defined in LTE for DL and uplink (UL)        data scheduling. For example, DCI formats 0 and 4 are used for        UL data scheduling while DCI formats 1, 1A, 1B, 1C, 1D, 2, 2A,        2B, 2C, 2D [3GPP TS 36.212 Technical Specification Group Radio        Access Network; Evolved Universal Terrestrial Radio Access        (E-UTRA); Multiplexing and channel coding (Release 13); V13.0.0        (2016-01)] are used for DL data scheduling. In DL, which DCI        format is used for data scheduling is associated with a DL        transmission scheme and/or the type of message to be        transmitted. The following are some of the transmission schemes        supported in LTE.    -   Single-antenna port    -   Transmit diversity (TxD)    -   Open-loop spatial multiplexing    -   Close-loop spatial multiplexing    -   Up to 8 layer transmission        The PDCCH is always transmitted with either the single-antenna        port or Transmit Diversity scheme while the PDSCH can use any        one of the transmission schemes. In LTE, a User Equipment (UE)        or wireless device (WD) is configured with a transmission mode        (TM), rather than a transmission scheme. There are 10 TMs, i.e.        TM1 to TM10, defined so far for the PDSCH in LTE. Each TM        defines a primary transmission scheme and a backup transmission        scheme. The backup transmission scheme is either single antenna        port or TxD.

The following is a list of some primary transmission schemes in LTE:

-   -   TM1: single antenna port, port 0    -   TM2: TxD    -   TM3: open-loop SM    -   TM4: close-loop SM    -   TM9: up to 8 layer transmission, port 7-14    -   TM10: up to 8 layer transmission, port 7-14        In TM1 to TM6, a cell specific reference signal (CRS) is used as        the reference signal for both channel state information feedback        and for demodulation at a WD. While in TM7 to TM10, a wireless        device specific demodulation reference signal (DMRS) is used as        the reference signal for demodulation.

The term wireless device or user equipment (a.k.a. UE) used herein mayrefer to any type of wireless device communicating with a network nodeand/or with another wireless device in a cellular or mobilecommunication system. Examples of a wireless device are target device,device to device (D2D) wireless device, machine type wireless device orwireless device capable of machine to machine (M2M) communication, PDA,iPAD, Tablet, mobile terminals, smart phone, laptop embedded equipped(LEE), laptop mounted equipment (LME), USB dongles etc.

Enhanced Physical Downlink Control Channel (EPDCCH)

Messages transmitted over the radio link to users can be broadlyclassified as control messages or data messages. Control messages areused to facilitate the proper operation of the system as well as properoperation of each wireless device within the system. Control messagescould include commands to control functions such as the transmittedpower from a WD, signalling of PRBs within which the data is to bereceived by the wireless device or transmitted from the wireless deviceand so on.

For wireless devices of Rel-11 or later, the wireless device can beconfigured to monitor the EPDCCH in addition to the PDCCH [3GPP TS36.211, 3GPP TS 36.213 Technical Specification Group Radio AccessNetwork; Evolved Universal Terrestrial Radio Access (E-UTRA); Physicallayer procedures (Release 13); V13.0.1 (2016-01)].

The enhanced physical downlink control channel (EPDCCH) was thusintroduced in Rel-11, in which 2, 4 or 8 PRB pairs in the data regionare reserved to exclusively contain EPDCCH transmissions, althoughexcluding from the PRB pair(s) the one to four first symbols that maycontain control information to wireless devices of releases earlier thanRel-11. See an illustration in FIG. 4.

Hence, the EPDCCH is frequency multiplexed with PDSCH transmissions incontrast to the PDCCH which is time multiplexed with PDSCHtransmissions. Note also that multiplexing of the PDSCH and any EPDCCHtransmission within a PRB pair is not supported in LTE Rel-11. Theadvantages of the EPDCCH over the PDCCH is that it allows support forincreased control channel capacity, support for improved spatial reuseof control channel resources, support for wireless device specificprecoding etc.

Furthermore, two modes of EPDCCH transmission are supported, thelocalized and the distributed EPDCCH transmission.

In distributed transmission, the EPDCCH is mapped to resource elementsin up to D PRB pairs, where D=2, 4, or 8. In this way, frequencydiversity can be achieved for the EPDCCH message. See FIG. 5 for anillustration of the concept of distributed transmission.

In localized transmission, an EPDCCH is mapped to one or two PRB pairsonly. For lower aggregation levels only one pair is used. In case theaggregation level of the EPDCCH is too large to fit the EPDCCH in onepair, the second PRB pair is used as well. See FIG. 6 for anillustration of localized transmission.

To facilitate the mapping of enhanced control channel elements (EECCEs)to physical resources, each PRB pair is divided into 16 enhancedresource element groups (EEREGs) and each EECCE is further divided intoN_(EREG) ^(ECCE)=4 or N_(EREG) ^(ECCE)=8 EREGs. For normal cyclic prefix(CP) and normal subframes, N_(EREG) ^(ECCE)=4 unless some conditions aremet as described in 3GPP TS 36.213. For extended CP and in some specialsubframes for Frame structure 2 (time division duplex (TDD)), N_(EREG)^(ECCE)=8 is used. An EPDCCH is consequently mapped to a multiple offour or eight EREGs depending on the aggregation level. Generally, anEPDCCH consists of L ECCEs, where L is the aggregation level. Thedifferent values of L supported in LTE are 1, 2, 4, 8, 16, 32 (the exactaggregation level allowed depends on which among the two modes of EPDCCHis chosen and other factors).

The EREG belonging to an EPDCCH resides in either a single PRB pair (asis typical for localized transmission) or a multiple of PRB pairs (as istypical for distributed transmission). The division of a PRB pair intoEREGs is illustrated in FIG. 7.

The EPDCCH uses demodulation reference signals (DMRS) for demodulation,shown in FIG. 7. There are 24 resource elements (RE) reserved for DMRSper PRB pair. For distributed EPDCCH, there are two DMRS antenna portsin each PRB pair, for normal cyclic prefix (CP), known as antenna ports107 and 109. These two ports are used for all distributed EPDCCHmessages in the PRB pair and provide two-fold antenna diversity (if thenetwork node chooses to transmit each port from a separate antenna,which is an implementation choice). For localized EPDCCH there are up tofour antenna ports 107-110 and each port is used by one EPDCCH messageonly in that PRB pair.

Port 107 uses 12 REs out of the 24 REs in the PRB pair, while port 109use the other 12 REs. Hence, the DMRS REs belonging to port 107 and 109are time and frequency multiplexed in the PRB pair. Port 107 and 108(and also port 109/110) on the other hand, use the same REs but are codemultiplexed by applying an orthogonal cover code (OCC) on top of 4 REson the same subcarrier. The OCC used for port 107-110 to createorthogonality are shown in the table below (from 3GPP TS 36.211).

TABLE 6.10.3A.2-1 from 3GPP TS 36.211: The sequence w _(p) (i) fornormal cyclic prefix Antenna port _(p) [w _(p) (0) w _(p) (1) w _(p) (2)w _(p) (3)] 107 [+1 +1 +1 +1] 108 [+1 −1 +1 −1] 109 [+1 +1 +1 +1] 110[+1 −1 +1 −1]For extended CP, only code multiplexed DMRS is used and the length twoOCC for port 107 and 108 are given in the table below, from 3GPP TS36.211.

TABLE 6.10.3A.2-2 from 3GPP TS 36.211: The sequence w _(p) (i) forextended cyclic prefix Antenna port _(p) [w _(p) (0) w _(p) (1)] 107 [+1+1] 108 [−1 +1]When receiving the distributed EPDCCH, the wireless device estimates thechannel in each DMRS RE and then it uses the OCC within each subcarrierand the corresponding three subcarriers within the PRB pair to obtainthe channel estimate for antenna port 107 and 109 respectively. Thesechannel estimates are then used when demodulating the EPDCCH.

Channel State Information Reference Signal (CSI-RS)

In LTE Release-10, a new channel state information reference signal(CSI-RS) was introduced for estimation of channel state information. TheCSI-RS based CSI feedback provides several advantages over theCell-Specific Reference Signal (CRS) based CSI feedback used in previousreleases. First, the CSI-RS is not used for demodulation of the datasignal, and thus does not require the same density (i.e., the overheadof the CSI-RS is substantially less). Second, CSI-RS provides a muchmore flexible means to configure CSI feedback measurements (e.g., whichCSI-RS resource to measure on can be configured in a wireless devicespecific manner).

Two types of CSI-RS are defined in LTE: non-zero power (NZP) CSI-RS andzero power (ZP) CSI-RS. NZP CSI-RS is transmitted by a network node (oreNB) for wireless devices to estimate the downlink channels to thenetwork node. For ZP CSI-RS, one or more CSI-RS resources are allocatedby the network node but nothing is transmitted on the resources. ZPCSI-RS can be used to reduce interferences to neighbour cells so thatbetter channel estimation can be performed by the wireless devices inthe neighbour cells.

For a Rel-13 wireless device, the number of supported antenna ports are1, 2, 4, 8, 12 and 16. In Rel-14, the antenna port numbers have beenincreased to include 20, 24, 28 and 32 ports. FIG. 8 shows the REsavailable for CSI-RS allocations in a PRB. Up to 40 REs can beconfigured for CSI-RS. CSI-RS is transmitted over all PRBs. Note thatCSI-RS signals are transmitted in all RBs of a system bandwidth, so thesame resource allocation is repeated in all RBs. In Rel-14 LTE, CSI-RScan also be transmitted with reduced density. That is, the CSI-RSsignals corresponding to different ports are transmitted in every N^(th)PRB.

CSI-RSs can be transmitted periodically on certain subframes, alsoreferred to as CSI-RS subframes. A CSI-RS subframe configurationconsists of a subframe periodicity and a subframe offset. Theperiodicity is configurable at 5, 10, 20, 40 and 80 ms. A CSI-RSconfiguration consists of a CSI-RS resource configuration as specifiedin Table 6.10.5.2-1 of 3GPP TS36.211 and a CSI-RS subframe configurationas specified in Table 6.10.5.3-1 of 3GPP TS36.211.

Codebook Based Channel State Information (CSI) Estimation and Feedback

In closed loop multiple-input and multiple-output (MIMO) transmissionschemes such as TM9 and TM10, a wireless device estimates and feeds backthe downlink CSI to the eNB. The evolved node B (eNB) base station usesthe feedback CSI to transmit downlink data to the WD. The CSI consistsof a transmission rank indicator (RI), a precoding matrix indicator(PMI) and a channel quality indicator(s) (CQI). A codebook of precodingmatrices is used by the wireless device to find the best match betweenthe estimated downlink channel and a precoding matrix in the codebookbased on certain criteria, for example, the wireless device throughput.The channel is estimated based on a Non-Zero Power CSI reference signal(NZP CSI-RS) transmitted in the downlink for TM9 and TM10.

The CQI/RI/PMI together provide the downlink channel state to the WD.This is also referred to as implicit CSI feedback since the estimationof the channel H_(n) is not fed back directly. The CQI/RI/PMI can bewideband (i.e., the whole transmission band) or sub band (i.e., parts ofthe whole transmission band) depending on which reporting mode isconfigured.

In LTE Rel-13, two types of CSI reporting were introduced, i.e. Class Aand Class B [3GPP TS 36.213 Technical Specification Group Radio AccessNetwork; Evolved Universal Terrestrial Radio Access (E-UTRA); Physicallayer procedures (Release 13); V13.0.1 (2016-01)]. In Class A CSIreporting, a wireless device measures and reports CSI based on a newcodebook for the configured 1-Dimensional or 2-Dimensional antenna arraywith 8, 12 or 16 antenna ports. The CSI consists of a rank indicator(RI), a PMI and a CQI or CQIs, similar to the CSI reporting in preRel-13. The Class A CSI reporting is extended to 20, 24, 28 and 32 portsin LTE Rel-14.

In Class B CSI reporting, in one scenario (referred to as “Class B K>”),multiple (i.e., K>1) CSI-RS resources can be configured for a wirelessdevice in a single CSI process. Each resource may be for multipleantenna ports (i.e. 1, 2, 4, or 8 ports). Each CSI-RS resource may beassociated with a precoded CSI-RS signal. A wireless device measuresdownlink CSIs associated with all the CSI-RS resources and selects thebest CSI among all the CSIs. The wireless device then reports back theselected CSI-RS Resource Indicator (CRI) and the corresponding CSI. Inanother scenario (also referred to as “Class B K=1”), a wireless deviceis configured with one CSI-RS resource, and the CSI-RS signals may beprecoded or “beamformed” particularly for the wireless device based onsome prior information about the wireless device such as uplink (UL)measurements. The wireless device then measures the downlink channelbased on the received CSI-RS signals on the CSI-RS resource and feedsback the estimated CSI to the eNB based on a new codebook for 2,4 or 8ports.

CSI Process

In LTE Release 11, the concept of a CSI process was introduced such thateach CSI process is associated with a NZP CSI-RS resource and aCSI-interference measurement (IM) resource. A CSI-IM resource is definedby a ZP CSI-RS resource and a ZP CSI-RS subframe configuration. Awireless device in TM10 can be configured with one or more (up to four)CSI processes per serving cell by higher layers and each CSI reported bythe wireless device corresponds to a CSI process. Multiple CSI processeswere introduced to support Coordinated Multi-Point (CoMP) transmissionin which a wireless device measures and feeds back CSI associated witheach transmission point (TP) to an eNB. Based on the received CSIs, theeNB may decide to transmit data to the wireless device from one of theTPs.

CSI Reporting

For CSI reporting, both periodic and aperiodic (i.e. triggered by eNB)reports are supported, known as P-CSI and A-CSI respectively. In a CSIprocess, a set of CSI-RS ports are configured for which the wirelessdevice performs measurements. These CSI-RS ports can be configured to beperiodically transmitted with 5 ms, 10 ms, 20 ms, etc., periodicity.

LTE Mechanisms for Control Signalling

LTE control signalling can be carried in a variety of ways, includingcarrying control information on the PDCCH or the PUCCH, embedded in thePUSCH, in medium access control (MAC) control elements (‘MAC CEs’), orin radio resource control (RRC) signalling. Each of these mechanisms iscustomized to carry a particular kind of control information.

Control information carried on the PDCCH, the PUCCH, or embedded in thePUSCH is physical layer related control information, such as downlinkcontrol information (DCI), and uplink control information (UCI), asdescribed in 3GPP TS 36.211, 36.212, and 36.213. DCI is generally usedto instruct the wireless device to perform some physical layer function,providing the needed information to perform the function. UCI generallyprovides the network with needed information, such as hybrid automaticrepeat request acknowledgement (HARQ-ACK), scheduling request (SR),channel state information (CSI), including CQI, PMI, RI, and/or CRI. UCIand DCI can be transmitted on a subframe-by-subframe basis, and so aredesigned to support rapidly varying parameters, including those that canvary with a fast fading radio channel. Because UCI and DCI can betransmitted in every subframe, UCI or DCI corresponding to a given celltend to be on the order of tens of bits, in order to limit the amount ofcontrol overhead.

Control information carried in MAC CEs is carried in MAC headers on theuplink and downlink shared transport channels (UL-SCH and DL-SCH), asdescribed in 3GPP TS 36.321 [3GPP TS 36.321 Technical SpecificationGroup Radio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA); Medium Access Control (MAC) protocol specification (Release13); V13.2.0 (2016-06)]. Since a MAC header does not have a fixed size,control information in MAC CEs can be sent when it is needed, and doesnot necessarily represent a fixed overhead. Furthermore, MAC CEs cancarry larger control payloads efficiently, since they are carried inUL-shared channel (SCH) or DL-SCH transport channels, which benefit fromlink adaptation, HARQ, and can be turbo coded (whereas UCI and DCI can'tbe in Rel-13). MAC CEs are used to perform repetitive tasks that use afixed set of parameters, such as maintaining timing advance or bufferstatus reporting, but these tasks generally do not require transmissionof a MAC CE on a subframe-by-subframe basis. Consequently, channel stateinformation related to a fast fading radio channel, such as PMI, CQI,RI, and contention resolution identity (CRI) are not carried in MAC CEsin Rel-13.

Rate Matching

In LTE, a virtual circular buffer is used to match any available coderate by selecting or pruning bits in the buffer. This rate matching isuseful since the number of available REs for a wireless device in asubframe may vary due to the presence or absence of various referencesignals. For example, the number of REs for the PDSCH in a subframeconfigured with CSI-RSs would be different from that in subframeswithout CSI-RSs. The rate matching can be used to adapt the variationsof the available PDSCH REs in this case. Note that in this case, boththe eNB and the wireless device knows the exact number of availablePDSCH REs and the RE locations in a RB. This PDSCH to RE mappinginformation is important for correct PDSCH decoding as otherwise, therecould be a mismatch between the REs a PDSCH is transmitted on and theREs over which the PDSCH is received and decoded.

PQI Bits in DCI 2D

In LTE Rel-11, a wireless device configured in transmission mode 10 fora given serving cell can be configured with up to four parameter sets byhigher layer signalling to decode the PDSCH according to a detectedPDCCH/EPDCCH with DCI format 2D intended for the wireless device and thegiven serving cell. This is because the eNB may transmit the PDSCH tothe wireless device via different transmission points (TPs) at differenttimes based on the channel conditions. There can be different referencesignals configured for different TPs. The wireless device shall use theparameter set according to the value of the ‘PDSCH RE Mapping andQuasi-Co-Location indicator’ (PQI) field (defined in Table 1, which isextracted from Table 7.1.9-1 in TS 36.213) in the detected PDCCH/EPDCCHwith DCI format 2D for determining the correct PDSCH RE mapping. Dynamicpoint selection (DPS) is a form of coordinated multi-point operation(CoMP) where the data transmission is from a single TP, where the TPthat transmits in a given time can change dynamically.

To support CoMP with DPS where the wireless device can receive thePDSCH, two ‘PQI’ bits in DCI format 2D are available for dynamicsignalling of the PDSCH mapping and quasi-co-location (QCL) information.This dynamic signalling targets adjusting transmission parameters andwireless device QCL assumptions so that they are compatible with thepotentially dynamically changing TP from which the PDSCH transmission inDPS originates. The QCL information provides the possibility for awireless device to exploit CRS and CSI-RS for, in terms of QCLproperties, aiding its demodulation of DMRS based PDSCH transmission.QCL properties make clear which properties of the channel may be assumedby the wireless device to be related between different antenna ports andare for TM10.

The parameters for determining PDSCH RE mapping are configured viahigher layer signalling for each parameter set, including

-   -   Number of CRS ports    -   CRS FreqShift.    -   ZP CSI-RS configuration

TABLE 1 PDSCH RE Mapping and Quasi-Co-Location Indicator field in DCIformat 2D Value of ′PDSCH RE Mapping and Quasi-Co- Location Indicator′field Description ′00′ Parameter set 1 configured by higher layers ′01′Parameter set 2 configured by higher layers ′10′ Parameter set 3configured by higher layers ′11′ Parameter set 4 configured by higherlayers

Puncturing

Puncturing can be another way of dealing with the variations of theavailable REs when a wireless device is unaware of the presence ofcertain reference signals in a subframe. For example, CSI-RS wasintroduced in LTE Rel-10 and a Rel-8 wireless device does not understandit. So, if a Rel-8 wireless device is scheduled, the PDSCH in a subframeconfigured with CSI-RS, the wireless device would think that the PDSCHis transmitted on the REs that are actually configured with CSI-RS. Inthis case, the eNB mutes the PDSCH transmission in those REs, or‘punctures’ the PDSCH signals in the REs, and the wireless device treatsthe received CSI-RS as the PDSCH. Of course, the decoding performancewould be degraded. However, as long as the number of REs are small, thedegradation can still be acceptable.

Aperiodic CSI-RS

In LTE Rel-14, it has been agreed [Chairman's notes, 3GPP RAN1 #86,section 7.2.4.1.2, Aug. 22-26, 2016. Gothenburg, Sweden] that aperiodicCSI-RS will be introduced, in which only CSI-RS resources are configuredfor a wireless device and unlike in the conventional CSI-RSconfiguration, there is no subframe configuration associated with it. Itwas agreed that a new “Aperiodic CSI-RS-Resource-Config IE” will bedefined in the Radio Resource Control (RRC) configuration. It wasfurther agreed that a wireless device can be preconfigured with K={1, 2,. . . , 8} CSI-RS resources.

One of the motivations for aperiodic CSI-RS is that the transmission ofCSI-RSs can occur in any subframe in order for a wireless device tomeasure and feedback downlink CSI, and it does not have to be limited toa set of preconfigured subframes. Another motivation is to be able toreduce CSI-RS overhead in the presence of a large number of wirelessdevices. For instance, if a large number of wireless devices arepresent, allocated periodic CSI-RS resources to each wireless device ina WD-specific manner will consume a large number of REs and will drivethe CSI-RS overhead up. The CSI-RS overhead can be reduced by aperiodicCSI-RS with a pool of CSI-RS resources where the pool can contain amaximum of K resources. The CSI-RS resource pool containing multipleCSI-RS resources can be shared among a group of wireless devices inwhich precoded or beamformed CSI-RS for targeting different wirelessdevices can be transmitted at different subframes by sharing the commonCSI-RS resource pool. The presence of aperiodic CSI-RS and CSImeasurement request can be dynamically triggered in DCI such as anuplink data grant message sent on the PDCCH or the EPDCCH to thetargeted wireless devices for CSI measurement and report. An example isshown in FIG. 9. In the dynamic aperiodic CSI-RS indication, thewireless device is told to measure CSI in the subframe it receives theindication and on which one of the preconfigured CSI-RS resources itshould measure CSI. The wireless device measures CSI on the indicatedCSI-RS resource and feeds back the CSI to the WD.

In some cases, not all K preconfigured CSI-RS resources may be needed ifthe load is varying. In this case a number N<K of CSI-RS resources maybe activated in a more dynamic way to cope with the varying load in thesystem. If N among the K CSI-RS resources are activated in the WD, thewireless device can expect to receive aperiodic CSI-RSs in one of the Nactivated CSI-RS resources. The activation of N out of K resources canbe done via MAC CE signalling.

One issue with this aperiodic CSI-RS transmission is potential collisionbetween REs used for the EPDCCH and the REs used for aperiodic CSI-RStransmission. As described above, the presence of aperiodic CSI-RS isdynamically triggered through DCI via an uplink grant message that couldbe sent on either the PDCCH or the EPDCCH. When possible, indicating thepresence of aperiodic CSI-RS dynamically via the EPDCCH (as opposed toindicating via the PDCCH) is desirable as it helps exploit theadditional advantages provided by the EPDCCH over the PDCCH. However,the wireless device should first decode the EPDCCH in a subframe beforeit can know that the aperiodic CSI-RS is transmitted in that subframe ornot. This creates a potential collision issue between the REs used forthe EPDCCH (similar to the ones shown in FIG. 7) and the REs foraperiodic CSI-RS (chosen from the REs shown in FIG. 8) in case aperiodicCSI-RS transmission in a subframe is indicated by the EPDCCH.

One way to resolve the collision issue is by puncturing the EPDCCH REswhen aperiodic CSI-RS is transmitted. A major drawback with thisapproach is that the number of REs used for aperiodic CSI-RS depends onthe load conditions and the number of active wireless devices. Underhigh load conditions where aperiodic CSI-RS gives the most gains overperiodic CSI-RS, the number of REs used for aperiodic CSI-RS could behigh. If the EPDCCH is punctured on a large number of REs, theperformance of the EPDCCH will be significantly degraded.

A second way to solve the collision issue is by specific configurationof a ZP CSI-RS for the EPDCCH, where the ZP CSI-RS configuration coversthe REs that could potentially be used for aperiodic CSI-RStransmission. When the wireless device decodes the EPDCCH, the wirelessdevice assumes that the EPDCCH is either rate matched around, orpunctured on, the REs contained in the ZP CSI-RS specifically configuredfor the EPDCCH. A drawback with this approach is that an additional ZPCSI-RS configuration (that is specifically used for rate matching orpuncturing purposes with the EPDCCH) need to be signalled to the WD.Additionally, if the EPDCCH indicates that an aperiodic CSI-RStransmission is present in the subframe then REs covered by theEPDCCH-specific ZP CSI-RS configuration can also contain aperiodicCSI-RS. This complicates the wireless device processing as it isgenerally desirable to indicate to the wireless device a ZP CSI-RSconfiguration that it uses to rate match all channels (including theEPDCCH and the PDSCH).

SUMMARY

In some embodiments, a method in a wireless device is provided. Themethod includes receiving the aperiodic CSI-RS based on the assumptionthat the aperiodic CSI-RS is not present in physical layer resourcescontained within the downlink control channel set. The method may alsoinclude receiving signalling to configure the wireless device with adownlink control channel set. The method may also include receiving fromthe network node on a physical control channel an indication of apresence of the aperiodic CSI-RS in a subframe.

In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in one of asubframe or a slot. In some embodiments, the indication of a presence ofthe aperiodic CSI-RS indicates that the aperiodic CSI-RS is present in apredetermined number of OFDM symbols.

In some embodiments, the aperiodic CSI-RS can be transmitted in thephysical layer resources in at least some defined conditions.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks,PRBs, corresponding to the downlink control channel set with which thewireless device is configured if the wireless device receives a downlinkcontrol channel message in the subframe that indicates that an aperiodicCSI-RS has been transmitted in the downlink control channel set. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message in thedownlink control channel set, then the wireless device assumes thataperiodic CSI-RS is transmitted in the subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel set. In someembodiments, a presence of the aperiodic CSI-RS in a subframe isindicated to the wireless device via a downlink control channel, such asPDCCH, and if the wireless device does not receive a downlink controlchannel message that indicates that the aperiodic CSI-RS has beentransmitted in the downlink control channel set, then the wirelessdevice assumes that the aperiodic CSI-RS is contained in the physicalresource blocks, PRBs, corresponding to the downlink control channel setin the subframe. In some embodiments, the wireless device assumes thatthe aperiodic CSI-RS is not transmitted in a subframe in the physicalresource blocks, PRBs, corresponding to the downlink control channel setwith which the wireless device is configured regardless of whether adownlink control channel message is received in the downlink controlchannel set.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe of physical resource blocks,PRBs, carrying a downlink control channel message to the wireless deviceif the wireless device receives a downlink control message in thesubframe that indicates that the aperiodic CSI-RS has been transmitted.In some embodiments, if a presence of the aperiodic CSI-RS in a subframeis indicated by a downlink control channel, such as PDCCH, and thewireless device does not receive a downlink control channel message,then the wireless device assumes the aperiodic CSI-RS is transmitted inthe subframe in the physical resource blocks, PRBs, corresponding to thedownlink control channel set with which the wireless device isconfigured. In some embodiments, the wireless device assumes that anetwork node does not transmit aperiodic CSI-RS in the physical resourceblocks, PRBs, carrying a downlink control channel message to thatwireless device if the wireless device receives a downlink controlchannel message that indicates that a aperiodic CSI-RS has beentransmitted in the subframe. In some embodiments, if a presence of theaperiodic CSI-RS in a subframe is indicated to the wireless device via adownlink control channel, such as PDCCH, and if the wireless device doesnot receive a downlink control channel message, then the wireless deviceassumes that aperiodic CSI-RS is transmitted to the wireless device inthe physical resource blocks, PRBs, corresponding to the downlinkcontrol channel set with which the wireless device is configured in thesubframe.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in any resource elements, REs,carrying a downlink control channel message to the wireless device ifthe wireless device receives a downlink control channel message in thesubframe. In some embodiments, if a presence of the aperiodic CSI-RS ina subframe is indicated by a downlink control channel, such as PDCCH,and the wireless device does not receive a downlink control channelmessage, then the wireless device assumes that the aperiodic CSI-RS canbe transmitted in the subframe in all resource elements, REs,corresponding to the downlink control channel set with which thewireless device is configured. In some embodiments, the wireless deviceassumes that aperiodic CSI-RS are not transmitted in a downlink pilottime slot in a case of frame structure type 2. In some embodiments, thewireless device assumes that aperiodic CSI-RS are not transmitted insubframes where transmission of the aperiodic CSI-RS would collide witha SystemInformationBlockType1 message. In some embodiments, the wirelessdevice assumes that aperiodic CSI-RS are not transmitted in physicalresource block pairs corresponding to the downlink control channel setwith which the wireless device is configured in the subframe.

In some embodiments, the wireless device assumes that aperiodic CSI-RSare not transmitted in physical resource block pairs carrying thedownlink control channel associated with a trigger of the aperiodicCSI-RS using an aperiodic trigger. In some embodiments, the wirelessdevice assumes that aperiodic CSI-RS are not transmitted in any resourceelements, RE, carrying the downlink control channel associated with atrigger of the aperiodic CSI-RS using an aperiodic trigger. In someembodiments, the downlink control channel is an enhanced physicaldownlink control channel, EPDCCH, and a downlink control channel messageis an EPDCCH message in a long term evolution communication system.

In some embodiments, a wireless device is provided. The wireless deviceincludes processing circuitry configured to receive the aperiodic CSI-RSbased on the assumption that the aperiodic CSI-RS is not present inphysical layer resources contained within the downlink control channelset. The processing circuitry may be further configured to receivesignalling from a network node to configure the wireless device with thedownlink control channel set and/or to receive from the network node ona physical control channel an indication of a presence of the aperiodicCSI-RS. The transceiver is further configured to

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks,PRBs, corresponding to the downlink control channel set with which thewireless device is configured if the wireless device receives a downlinkcontrol channel message in the subframe that indicates that an aperiodicCSI-RS has been transmitted in the downlink control channel set. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message in thedownlink control channel set, then the wireless device assumes thataperiodic aperiodic CSI-RS is transmitted in the subframe in thephysical resource blocks, PRBs, corresponding to the downlink controlchannel set. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device via a downlink controlchannel, such as PDCCH, and if the wireless device does not receive adownlink control channel message that indicates that the aperiodicCSI-RS has been transmitted in the downlink control channel set, thenthe wireless device assumes that the aperiodic CSI-RS is contained inthe physical resource blocks, PRBs, corresponding to the downlinkcontrol channel set in the subframe.

In some embodiments, the wireless device assumes that aperiodic CSI-RSis not transmitted in a subframe in the physical resource blocks, PRBs,corresponding to the downlink control channel set with which thewireless device is configured regardless of whether a downlink controlchannel message is received in the downlink control channel set. In someembodiments, the wireless device assumes that the aperiodic CSI-RS isnot transmitted in a subframe of physical resource blocks, PRBs,carrying a downlink control channel message to the wireless device ifthe wireless device receives a downlink control message in the subframethat indicates that the aperiodic CSI-RS has been transmitted. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message, then thewireless device assumes the aperiodic CSI-RS is transmitted in thesubframe in the physical resource blocks, PRBs, corresponding to thedownlink control channel set with which the wireless device isconfigured.

In some embodiments, the wireless device assumes that a network nodedoes not transmit aperiodic CSI-RS in the physical resource blocks,PRBs, carrying a downlink control channel message to that wirelessdevice if the wireless device receives a downlink control channelmessage that indicates that a aperiodic CSI-RS has been transmitted inthe subframe. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device via a downlink controlchannel, such as PDCCH, and if the wireless device does not receive adownlink control channel message, then the wireless device assumes thataperiodic CSI-RS is transmitted to the wireless device in the physicalresource blocks, PRBs, corresponding to the downlink control channel setwith which the wireless device is configured in the subframe. In someembodiments, the wireless device assumes that the aperiodic CSI-RS isnot transmitted in a subframe in any resource elements, REs, carrying adownlink control channel message to the wireless device if the wirelessdevice receives a downlink control channel message in the subframe. Insome embodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message, then thewireless device assumes that the aperiodic CSI-RS can be transmitted inthe subframe in all resource elements, REs, corresponding to thedownlink control channel set with which the wireless device isconfigured.

In some embodiments, the wireless device assumes that aperiodic CSI-RSare not transmitted in a downlink pilot time slot in a case of framestructure type 2. In some embodiments, the wireless device assumes thataperiodic CSI-RS are not transmitted in subframes where transmission ofthe aperiodic CSI-RS would collide with a SystemInformationBlockType1message. In some embodiments, the wireless device assumes that aperiodicCSI-RS are not transmitted in physical resource block pairscorresponding to the downlink control channel set with which thewireless device is configured in the subframe. In some embodiments, thewireless device assumes that aperiodic CSI-RS are not transmitted inphysical resource block pairs carrying the downlink control channelassociated with a trigger of the aperiodic CSI-RS using an aperiodictrigger. In some embodiments, the wireless device assumes that aperiodicCSI-RS are not transmitted in any resource elements, RE, carrying thedownlink control channel associated with a trigger of the aperiodicCSI-RS using an aperiodic trigger. In some embodiments, the downlinkcontrol channel is an enhanced physical downlink control channel,EPDCCH, and a downlink control channel message is an EPDCCH message in along term evolution communication system.

In some embodiments, a wireless device configured to avoid collisionbetween downlink control channel and a channel state informationreference signal, aperiodic CSI-RS, is provided. The wireless deviceincludes a downlink control channel set configuration receiver moduleconfigured to receive signalling from a network node to configure thewireless device with a downlink control channel set. The wireless devicealso includes a downlink control channel set configuration moduleconfigured to configure the wireless device with a downlink controlchannel set according to signalling received from a network node. Thewireless device further includes a aperiodic CSI-RS indication receivermodule configured to receive from the network node on a physical controlchannel an indication of a presence of the aperiodic CSI-RS in asubframe. The wireless device also includes a aperiodic CSI-RS receivermodule configured to receive the aperiodic CSI-RS based on theassumption that the aperiodic CSI-RS is not present in physical layerresources contained within the downlink control channel set.

In some embodiments, a method in a network node is provided. The methodincludes signalling a wireless device to configure the wireless devicewith a downlink control channel set that does not contain a aperiodicCSI-RS. The method also includes signalling to the wireless device aaperiodic CSI-RS, the presence of the aperiodic CSI-RS in a downlinkchannel so as to enable the wireless device to assume that the aperiodicCSI-RS is not present in physical layer resources contained within thedownlink control channel set.

In some embodiments, the network node does not transmit the aperiodicCSI-RS to the wireless device in a subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel setconfigured to the wireless device. In some embodiments, the network nodeindicates a presence of the aperiodic CSI-RS in the subframe and thewireless device does not assume that the aperiodic CSI-RS is not presentin the downlink control channel set. In some embodiments, the networknode indicates a presence of the aperiodic CSI-RS in the subframe andtransmits the aperiodic CSI-RS in the subframe in all resource elementscorresponding to the downlink control channel set.

In some embodiments, a network node is provided. The network nodeincludes processing circuitry configured to signal to a wireless deviceto configure the wireless device with a downlink control channel setthat does not contain a aperiodic CSI-RS. The transceiver is configuredto signal to the wireless device a aperiodic CSI-RS, the presence of theaperiodic CSI-RS in a downlink channel so as to enable the wirelessdevice to assume that the aperiodic CSI-RS is not present in physicallayer resources contained within the downlink control channel set.

In some embodiments, the network node does not transmit the aperiodicCSI-RS to the wireless device in a subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel setconfigured to the wireless device. In some embodiments, the network nodeindicates a presence of the aperiodic CSI-RS in the subframe and thewireless device does not assume that the aperiodic CSI-RS is not presentin the downlink control channel set. In some embodiments, the networknode indicates a presence of the aperiodic CSI-RS in the subframe andtransmits the aperiodic CSI-RS in the subframe in all resource elementscorresponding to the downlink control channel set.

In some embodiments, a network node is provided. The network nodeincludes a transceiver module configured to signal to a wireless deviceto configure the wireless device with a downlink control channel setthat does not contain a aperiodic CSI-RS. The transceiver module is alsoconfigured to signal to the wireless device a aperiodic CSI-RS, thepresence of the aperiodic CSI-RS being in a subframe in a downlinkchannel so as to enable the wireless device to assume that the aperiodicCSI-RS is not present in physical layer resources contained within thedownlink control channel set.

In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in one of asubframe or a slot. In some embodiments, the indication of a presence ofthe aperiodic CSI-RS indicates that the aperiodic CSI-RS is present in apredetermined number of OFDM symbols.

In some embodiments, the aperiodic CSI-RS can be transmitted in thephysical layer resources in at least some defined conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic diagram illustrating a LTE downlink physicalresource;

FIG. 2 is a schematic diagram illustrating a LTE time-domain structure;

FIG. 3 is a schematic diagram illustrating a downlink subframe;

FIG. 4 is a schematic diagram illustrating a downlink subframe showing10 RB pairs and configuration of three EPDCCH regions of size 1 PRB paireach, the remaining PRB pairs can be used for PDSCH transmissions;

FIG. 5 is a schematic diagram illustrating a downlink subframe showing 4parts, an enhanced resource element group (EREG), belonging to an EPDCCHbeing mapped to multiples of the enhanced control regions known as PRBpairs in an EPDCCH set, to achieve distributed transmission andfrequency diversity;

FIG. 6 is a schematic diagram illustrating a downlink subframe showingthe 4 ECCEs belonging to an EPDCCH are mapped to one of the enhancedcontrol regions, to achieve localized transmission;

FIG. 7 is a schematic diagram illustrating a PRB pair of normal cyclicprefix configuration in a normal subframe, where the shaded un-numberedsquares contain the demodulation reference signals (DMRS); each numberedsquare being a resource element in which the number corresponds to theEREG it belongs to; the shaded numbered squares corresponding to the RDbelonging to the same EREG indexed with 0, etc.;

FIG. 8 is a schematic diagram illustrating resources available forCSI-RS allocation in a PRB in a CSI-RS subframe;

FIG. 9 is a schematic diagram illustrating an aperiodic CSI-RStransmission;

FIG. 10 is a block diagram of a wireless communication systemconstructed according to principles set forth herein;

FIG. 11 is a block diagram of a network node constructed according toprinciples set forth herein;

FIG. 12 is a block diagram of an alternative embodiment of a networknode constructed according to principles set forth herein;

FIG. 13 is a block diagram of a wireless device constructed according toprinciples set forth herein;

FIG. 14 is a block diagram of an alternative embodiment of a wirelessdevice constructed according to principles set forth herein;

FIG. 15 is an example of an embodiment where the wireless device assumesaperiodic CSI-RS is not transmitted in a given subframe in the PRBsbelonging to an EPDCCH set containing EPDCCH message in that subframe;

FIG. 16 is flowchart of an exemplary process for determining when anaperiodic CSI-RS is transmitted in PRBs belonging to the EPDCCH set in acurrent subframe;

FIG. 17 is a flowchart of an exemplary process for determining that anaperiodic CSI-RS is not transmitted in PRBs belonging to the EPDCCH setin a current subframe;

FIG. 18 is an example of an embodiment where the WD assumes aperiodicCSI-RS is not transmitted in a given subframe in the PRBs carrying anEPDCCH message;

FIG. 19 is a flowchart of an exemplary process for determining when anaperiodic CSI-RS is transmitted in PRBs carrying an EPDCCH message in acurrent subframe

FIG. 20 is a flowchart of an exemplary process for determining when anaperiodic CSI-RS is transmitted in PRBs carrying an EPDCCH message in acurrent subframe;

FIG. 21 is an example of an EPDCCH configuration to reduce impact on CSIestimation when aperiodic CSI-RS is not transmitted in the PRBsconfigured for EPDCCH; and

FIG. 22 is a flowchart of an exemplary process in a network node foravoiding collisions between a downlink control channel and a channelstate information reference signal;

FIG. 23 is a flowchart of an exemplary process in a wireless device foravoiding collisions between a downlink control channel and a channelstate information reference signal; and

FIG. 24 is a flowchart of an exemplary process in a wireless deviceconstructed in accordance principles set forth herein.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to avoiding collision between enhanced physicaldownlink control channel (EPDCCH) and aperiodic channel stateinformation reference signals (CSI-RS). Accordingly, components havebeen represented where appropriate by conventional symbols in thedrawings, showing only those specific details that are pertinent tounderstanding the embodiments so as not to obscure the disclosure withdetails that will be readily apparent to those of ordinary skill in theart having the benefit of the description herein.

Accordingly, components have been represented where appropriate byconventional symbols in the drawings, showing only those specificdetails that are pertinent to understanding the embodiments so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having the benefit of the descriptionherein.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements.

Note that although terminology from 3GPP LTE has been used in thisdisclosure, this should not be seen as limiting the scope of thedisclosure to only the aforementioned system. Other wireless systems,including but not limited to Wide Band Code Division Multiple Access(WCDMA), Worldwide Interoperability for Microwave Access (WiMax), UltraMobile Broadband (UMB) and Global System for Mobile Communications(GSM), may also benefit from exploiting the ideas covered within thisdisclosure.

Also note that terminology such as eNodeB and wireless device should beconsidering non-limiting and does in particular not imply a certainhierarchical relation between the two; in general “eNodeB” could beconsidered as a first device and “UE” a second device, and these twodevices communicate with each other over some radio channel. Herein, wealso focus on wireless transmissions in the downlink, but implementationand the functions and concepts described herein are equally applicablein the uplink.

In order to improve aperiodic CSI-RS resource efficiency while at thesame time reducing average CSI triggering delay (see R1-167637, “UEspecific Beamforming with Aperiodic CSI-RS Transmission”, Ericsson, 3GPPTSG-RAN WG1 #86, Gothenburg, Sweden, Aug. 22-26, 2016, for details), theK CSI-RS resources without ‘Subframe_config’ need to be dynamicallyshared among multiple wireless devices.

A problem with the introduction of aperiodic CSI-RS transmission is thepotential collision between REs used for EPDCCH and the REs used foraperiodic CSI-RS transmission. As described above, the presence ofaperiodic CSI-RS is dynamically triggered via DCI via an uplink grantmessage that could be sent on either the PDCCH or the EPDCCH. Whenpossible, indicating the presence of aperiodic CSI-RS dynamically viathe EPDCCH (as opposed to indicating via the PDCCH) is desirable as ithelps exploit the additional advantages provided by the EPDCCH over thePDCCH. However, the wireless device should first decode the EPDCCH in asubframe before it can know that the aperiodic CSI-RS is transmitted inthat subframe or not. This creates a potential collision problem betweenthe REs used for EPDCCH (similar to the ones shown in FIG. 7) and theREs for aperiodic CSI-RS (chosen from the REs shown in FIG. 8) in caseaperiodic CSI-RS transmission in a subframe is indicated by the EPDCCH.

One way to resolve the collision issue is by puncturing the EPDCCH REswhen aperiodic CSI-RS is transmitted. A major drawback with thisapproach is that the number of REs used for aperiodic CSI-RS depends onthe load conditions and the number of active wireless devices. Underhigh load conditions where aperiodic CSI-RS gives the most gains overperiodic CSI-RS, the number of REs used for aperiodic CSI-RS could behigh. If the EPDCCH is punctured on a large number of REs, theperformance of the EPDCCH will be significantly degraded.

A second way to solve the collision issue is by specifically configuringa ZP CSI-RS for the EPDCCH, where the ZP CSI-RS configuration covers theREs that could potentially be used for aperiodic CSI-RS transmission.When the wireless device decodes the EPDCCH, the wireless device assumesthat the EPDCCH is either rate matched around or punctured on the REscontained in the ZP CSI-RS specifically configured for EPDCCH. Thedrawback with this approach is that an additional ZP CSI-RSconfiguration (that is specifically used for rate matching or puncturingpurposes with EPDCCH) needs to be signalled to the WD. Additionally, ifthe EPDCCH indicates that an aperiodic CSI-RS transmission is present inthe subframe, then REs covered by the EPDCCH-specific ZP CSI-RSconfiguration can also contain aperiodic CSI-RS. This complicates thewireless device processing as it is generally desirable to indicate tothe wireless device a ZP CSI-RS configuration that it uses to rate matchall channels (including the EPDCCH and the PDSCH).

To alleviate the drawbacks of these existing solutions, the followingsolutions are proposed herein.

In one solution, to avoid collision between the EPDCCH and aperiodicCSI-RS, the wireless device can assume that aperiodic CSI-RSs are nottransmitted in a subframe where the wireless device is monitoring theEPDCCH, within the PRBs belonging to an EPDCCH set or sets configured tothe WD, if the wireless device receives an EPDCCH message in any of theconfigured EPDCCH sets in the subframe. In another variant of the firstsolution, the wireless device can assume that aperiodic CSI-RS is nottransmitted in the PRBs belonging to an EPDCCH set configured to thatwireless device in a subframe regardless of whether a valid EPDCCHmessage is received for that particular wireless device or not in theEPDCCH set and in the subframe. The CSI-RS is still transmitted by thenetwork node in PRBs outside the EPDCCH set configured to the wirelessdevice mentioned above, and the wireless device can therefore make thecorresponding CSI measurements on those CSI-RSs outside the mentionedEPDCCH set(s).

Note that an EPDCCH message is valid for the wireless device if thewireless device successfully decodes the message with the C-RNTI (radionetwork temporary identifier) to which the wireless device has beenassigned. The C-RNTI is encoded in the CRC (cyclic redundancy check),and if the CRC fails, the wireless device discards the EPDCCH message,but if the CRC matches the message is intended for the wireless deviceand the message is valid. The wireless device will in this case takeaction on the content of the message which may contain the trigger ofthe aperiodic CSI-RS.

In a second solution, the wireless device can assume that aperiodicCSI-RSs are not transmitted in a subframe, within the PRBs carrying anEPDCCH message to the wireless device if the wireless device receives anEPDCCH message in the subframe that indicates an aperiodic CSI-RS hasbeen transmitted. Particularly, the wireless device thus does notmeasure CSI-RS in those PRB for which it received the valid EPDCCHmessage containing the trigger of the aperiodic CSI-RS in the samesubframe.

In a third solution, the wireless device can assume that aperiodicCSI-RS is not transmitted in a subframe in any REs carrying an EPDCCHmessage to the wireless device if the wireless device receives an EPDCCHmessage in the subframe that indicates an aperiodic CSI-RS has beentransmitted. Particularly, the wireless device thus does not measureCSI-RS in those RE for which it received the valid EPDCCH messagecontaining the trigger of the aperiodic CSI-RS in the same subframe.

The main advantages of the proposed solutions are simplified wirelessdevice processing, alleviating the need to signal the wireless devicewith additional ZP CSI-RS configurations that are specific to EPDCCHonly, and maintaining good EPDCCH performance by avoiding puncturing ofEPDCCH REs.

Returning to the drawing figures, in which like elements are referred toby like reference numerals, there is shown in FIG. 10 a block diagram ofa wireless communication system 10 constructed according to principlesset forth herein. The wireless communication network 10 includes a cloud12 which may include the Internet and/or the public switched telephonenetwork (PSTN). Cloud 12 may also serve as a backhaul network of thewireless communication network 10. The wireless communication network 10includes one or more network nodes 14A and 14B, which may communicatedirectly via an X2 interface in LTE embodiments, and are referred tocollectively as network nodes 14. It is contemplated that otherinterface types can be used for communication between network nodes 14for other communication protocols such as New Radio (NR). The networknodes 14 may serve wireless devices 16A and 16B, referred tocollectively herein as wireless devices 16. Note that, although only twowireless devices 16 and two network nodes 14 are shown for convenience,the wireless communication network 10 may typically include many morewireless devices (WDs) 16 and network nodes 14. Further, in someembodiments, WDs 16 may communicate directly using what is sometimesreferred to as a side link connection.

The term “wireless device” or mobile terminal used herein may refer toany type of wireless device communicating with a network node 14 and/orwith another wireless device 16 in a cellular or mobile communicationsystem 10. Examples of a wireless device 16 are user equipment (UE),target device, device to device (D2D) wireless device, machine typewireless device or wireless device capable of machine to machine (M2M)communication, PDA, tablet, smart phone, laptop embedded equipped (LEE),laptop mounted equipment (LME), USB dongle, etc.

The term “network node” used herein may refer to any kind of radio basestation in a radio network which may further comprise any basetransceiver station (BTS), base station controller (BSC), radio networkcontroller (RNC), evolved Node B (eNB or eNodeB), NR gNodeB, NR gNB,Node B, multi-standard radio (MSR) radio node such as MSR BS, relaynode, donor node controlling relay, radio access point (AP),transmission points, transmission nodes, Remote Radio Unit (RRU) RemoteRadio Head (RRH), nodes in distributed antenna system (DAS), etc.

Although embodiments are described herein with reference to certainfunctions being performed by network node 14, it is understood that thefunctions can be performed in other network nodes and elements. It isalso understood that the functions of the network node 14 can bedistributed across network cloud 12 so that other nodes can perform oneor more functions or even parts of functions described herein.

As shown in FIG. 10, the network node 14 includes a transmitter 18configured to transmit a downlink control channel set configuration to awireless device 16. The wireless device 16 includes a receiver 20configured to receive the downlink control channel set configurationfrom the network node 14

A block diagram of a network node 14 is shown in FIG. 11. The networknode 14 has processing circuitry 22. In some embodiments, the processingcircuitry may include a memory 24 and processor 26, the memory 24containing instructions which, when executed by the processor 26,configure processor 26 to perform the one or more functions describedherein. In addition to a traditional processor and memory, processingcircuitry 22 may comprise integrated circuitry for processing and/orcontrol, e.g., one or more processors and/or processor cores and/orFPGAs (Field Programmable Gate Array) and/or ASICs (Application SpecificIntegrated Circuitry).

Processing circuitry 22 may include and/or be connected to and/or beconfigured for accessing (e.g., writing to and/or reading from) memory24, which may include any kind of volatile and/or non-volatile memory,e.g., cache and/or buffer memory and/or RAM (Random Access Memory)and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM(Erasable Programmable Read-Only Memory). Such memory 24 may beconfigured to store code executable by control circuitry and/or otherdata, e.g., data pertaining to communication, e.g., configuration and/oraddress data of nodes, etc. Processing circuitry 22 may be configured tocontrol any of the methods described herein and/or to cause such methodsto be performed, e.g., by processor 26. Corresponding instructions maybe stored in the memory 24, which may be readable and/or readablyconnected to the processing circuitry 22. In other words, processingcircuitry 22 may include a controller, which may comprise amicroprocessor and/or microcontroller and/or FPGA (Field-ProgrammableGate Array) device and/or ASIC (Application Specific Integrated Circuit)device. It may be considered that processing circuitry 22 includes ormay be connected or connectable to memory, which may be configured to beaccessible for reading and/or writing by the controller and/orprocessing circuitry 22.

The memory 24 is configured to store CSI-RS parameters which may includea CSI-RS configuration and/or a CSI-RS subframe configuration, asmentioned above. A transceiver 28 has a downlink control channel setconfiguration transmitter 18 configured to transmit a downlink controlchannel set to the wireless device 16 by which the wireless device is tobe configured. The transceiver 28 also includes a CSI-RS transmitter 32(which may be the same transmitter as transmitter 18) configured totransmit a CSI-RS to the wireless device 16, the presence of the CSI-RSbeing in a subframe in a downlink channel so as to enable the wirelessdevice to assume that the CSI-RS is not present in physical layerresources contained within the downlink control channel set.

FIG. 12 is a block diagram of an alternative embodiment of a networknode 14 configured according to principles set forth herein for avoidingcollision between a downlink control channel and a channel stateinformation reference signal. The network node 14 includes a memorymodule 25 configured to store CSI-RS parameters. The network node 14further includes a transceiver module 29 that includes the downlinkcontrol channel set configuration transmitter 18 and the CSI-RStransmitter 32. Some functions of the transceiver module 29 may beimplemented at least in part by the processor 26.

FIG. 13 is a block diagram of a wireless device 16. The wireless device16 has processing circuitry 42. In some embodiments, the processingcircuitry may include a memory 44 and processor 46, the memory 44containing instructions which, when executed by the processor 46,configure processor 46 to perform the one or more functions describedherein. In addition to a traditional processor and memory, processingcircuitry 42 may comprise integrated circuitry for processing and/orcontrol, e.g., one or more processors and/or processor cores and/orFPGAs (Field Programmable Gate Array) and/or ASICs (Application SpecificIntegrated Circuitry).

Processing circuitry 42 may include and/or be connected to and/or beconfigured for accessing (e.g., writing to and/or reading from) memory44, which may include any kind of volatile and/or non-volatile memory,e.g., cache and/or buffer memory and/or RAM (Random Access Memory)and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM(Erasable Programmable Read-Only Memory). Such memory 44 may beconfigured to store code executable by control circuitry and/or otherdata, e.g., data pertaining to communication, e.g., configuration and/oraddress data of nodes, etc. Processing circuitry 42 may be configured tocontrol any of the methods described herein and/or to cause such methodsto be performed, e.g., by processor 46. Corresponding instructions maybe stored in the memory 44, which may be readable and/or readablyconnected to the processing circuitry 42. In other words, processingcircuitry 42 may include a controller, which may comprise amicroprocessor and/or microcontroller and/or FPGA (Field-ProgrammableGate Array) device and/or ASIC (Application Specific Integrated Circuit)device. It may be considered that processing circuitry 42 includes ormay be connected or connectable to memory, which may be configured to beaccessible for reading and/or writing by the controller and/orprocessing circuitry 42.

The memory 44 is configured to store CSI-RS parameters which may includea CSI-RS configuration and/or a CSI-RS subframe configuration asmentioned above. The processor 46 is configured to configure thewireless device 16 with a downlink control channel configuration set viaa downlink control channel configuration unit 52. A transceiver 48 has adownlink control channel set configuration receiver 20 configured totransmit a downlink control channel set to the wireless device 16 bywhich the wireless device is to be configured. The transceiver 48 alsoincludes a CSI-RS indicator receiver 54 configured to receive from thenetwork node on a physical control channel an indication of a presenceof the CSI-RS in a subframe. The transceiver 48 also includes a CSI-RSreceiver 56 (which may be the same receiver as the receiver 20)configured to transmit a CSI-RS to the wireless device 16, the presenceof the CSI-RS being in a subframe in a downlink channel so as to enablethe wireless device to assume that the CSI-RS is not present in physicallayer resources contained within the downlink control channel set.

FIG. 14 is a block diagram of an alternative embodiment of a wirelessdevice 16 configured according to principles set forth herein foravoiding collision between a downlink control channel and a channelstate information reference signal. The wireless device 16 includes amemory module 45 configured to store CSI-RS parameters. The wirelessdevice 16 also includes a downlink control channel set configurationmodule 53 that may be implemented as software executable by theprocessor 46. The wireless device also includes a CSI-RS indicationreceiver 55 configured to receive from the network node on a physicalcontrol channel an indication of a presence of the CSI-RS in a subframe.The wireless device 16 further includes a transceiver module 49 thatincludes the downlink control channel set configuration receiver 20 andthe CSI-RS receiver 57. Some functions of the transceiver module 49 maybe implemented at least in part by the processor 46.

Embodiment 1

One solution to resolve the collision between EPDCCH REs and REsbelonging to Aperiodic CSI-RS transmission is to let the wireless deviceassume that aperiodic CSI-RSs are not transmitted in a subframe in thePRBs belonging to an EPDCCH set configured to that wireless device ifthe wireless device receives an EPDCCH message that indicates that anaperiodic CSI-RS has been transmitted in that EPDCCH set in thesubframe. If the presence of aperiodic CSI-RS transmission in a subframeis indicated by the PDCCH and the wireless device does not receive anEPDCCH message in an EPDCCH set, then the wireless device is allowed toassume that aperiodic CSI-RS is transmitted in the subframe in the PRBsbelonging to that EPDCCH set. It should be noted that these rules applyonly when the wireless device is configured to receive aperiodic CSI-RSwhich has no subframe configuration associated with it (i.e., the rulesdo not apply to wireless devices not configured to receive aperiodicCSI-RS transmission). An example of this embodiment is shown in FIG. 15.The steps related to this embodiment are illustrated in FIG. 16.

FIG. 16 is a flowchart of an exemplary process performed by a wirelessdevice 16 of avoiding collision between a downlink control channel and achannel state information reference signal. The process includesdetermining whether an EPDCCH message is received, via the receiver 20,in an EPDCCH set in a current subframe, where the message that indicatesan aperiodic CSI-RS has been transmitted by the transmitter 32 (blockS100). If so, the process includes determining whether an aperiodicCSI-RS is present in the current subframe (block S102). If so, thewireless device 16 assumes an aperiodic CSI-RS is not transmitted inPRBs belonging to the EPDCCH set in the current subframe (block S104).Returning to block S100, if the EPDCCH message is not received in anEPDCCH set in the current subframe indicating that an aperiodic CSI-RShas been transmitted, then a determination is made whether an aperiodicCSI-RS is present in the current subframe (block S106). If so, thewireless device 16 assumes that an aperiodic CSI-RS is transmitted, viathe transmitter 32, in PRBs belonging to the EPDCCH set in the currentsubframe (block S108).

In some variants of the embodiment, the network node 14 does nottransmit aperiodic CSI-RS to a wireless device in a subframe in the PRBsbelonging to an EPDCCH set configured to that wireless device if thewireless device receives an EPDCCH message in that EPDCCH set in thesubframe. If the presence of aperiodic CSI-RS transmission in a subframeis indicated to the wireless device by the network node 14 via the PDCCHand that the wireless device does not receive an EPDCCH message thatindicates an aperiodic CSI-RS has been transmitted in an EPDCCH set,then the wireless device may assume that the network node 14 transmitsaperiodic CSI-RS to the wireless device in the PRBs belonging to thatEPDCCH set in the subframe.

In an alternate embodiment, if a wireless device is configured withEPDCCH sets and is configured to receive aperiodic CSI-RS, then thewireless device can assume that aperiodic CSI-RS is not transmitted in asubframe in the PRBs belonging to an EPDCCH set configured to thatwireless device 16 regardless of whether an EPDCCH message is receivedor not in the EPDCCH set. In some variants, the network node 14 does nottransmit aperiodic CSI-RS to a wireless device 16 in a subframe in thePRBs belonging to an EPDCCH set configured to that wireless device 16.The steps related to this alternate embodiment are illustrated in FIG.17.

FIG. 17 is a flowchart of an alternate process in a wireless device 16of an exemplary process performed by a wireless device 16 of avoidingcollision between a downlink control channel and a channel stateinformation reference signal. The process includes configuring thewireless device 16 with EPDCCH sets received by the receiver 20 and isconfigured to receive aperiodic CSI-RS via the receiver 52 (block S10).The process also includes the wireless device 16 assuming that aperiodicCSI-RS is not transmitted in PRBs belonging to the EPDCCH set in thecurrent subframe (block S112).

Embodiment 2

A second solution to resolve the collision between EPDCCH REs and REsbelonging to aperiodic CSI-RS transmission is to let the wireless deviceassume that aperiodic CSI-RS is not transmitted in a subframe in thePRBs carrying an EPDCCH message to that wireless device if the wirelessdevice receives an EPDCCH message that indicates an aperiodic CSI-RS hasbeen transmitted in the subframe. If the presence of aperiodic CSI-RStransmission in a subframe is indicated by the PDCCH and the wirelessdevice 16 does not receive an EPDCCH message, then the wireless device16 is allowed to assume that aperiodic CSI-RS is transmitted in thesubframe in the PRBs belonging to the EPDCCH sets configured to the WD.It should be noted that these rules apply only when the wireless device16 is configured to receive aperiodic CSI-RS which has no subframeconfiguration associated with it (i.e., the rules do not apply towireless devices not configured to receive aperiodic CSI-RStransmission). An example of this embodiment is shown in FIG. 18. Thesteps related to this embodiment are illustrated in FIG. 19.

FIG. 19 is a flowchart of an exemplary process performed by a wirelessdevice 16 of avoiding collision between a downlink control channel andan aperiodic channel state information reference signal. The processincludes determining, via the downlink control channel set configurationunit 52, whether an EPDCCH message is received in an EPDCCH set in acurrent subframe, where the message that indicates an aperiodic CSI-RShas been transmitted (block S114). If so, the process includesdetermining whether an aperiodic CSI-RS is present in the currentsubframe (block S116). If so, the wireless device 16 assumes anaperiodic CSI-RS is not transmitted in PRBs carrying an EPDCCH messagein the current subframe (block S118). Returning to block S114, if theEPDCCH message is not received in an EPDCCH set in the current subframeindicating that aperiodic CSI-RS has been transmitted, then adetermination is made whether an aperiodic CSI-RS is present in thecurrent subframe (block S120). If so, the wireless device 16 assumes anaperiodic CSI-RS can be transmitted in PRBs belonging to the EPDCCH setsin the current subframe (block S122).

In some variants of the embodiment, the wireless device 16 may assumethat the network node does not transmit aperiodic CSI-RS in the PRBscarrying an EPDCCH message to that wireless device if the wirelessdevice receives an EPDCCH message that indicates an aperiodic CSI-RS hasbeen transmitted in the subframe. If the presence of aperiodic CSI-RStransmission in a subframe is indicated to the wireless device 16 by thenetwork node 14 via the PDCCH and that the wireless device 16 does notreceive an EPDCCH message, then the wireless device 16 may assume thatthe network node 14 transmits aperiodic CSI-RS to the wireless device inthe PRBs belonging to the EPDCCH sets configured to the wireless device16 in the subframe.

Embodiment 3

A third solution to resolve the collision between EPDCCH REs and REsbelonging to aperiodic CSI-RS transmission is to let the wireless deviceassume that aperiodic CSI-RS is not transmitted in a subframe in any REscarrying an EPDCCH message to that wireless device 16 if the wirelessdevice 16 receives an EPDCCH message in the subframe. For instance, ifthe REs with index 0 shown in FIG. 7 carry an EPDCCH message, and thewireless device 16 assumes that aperiodic CSI-RS is not transmitted inthese REs. If the presence of aperiodic CSI-RS transmission in asubframe is indicated by the PDCCH and the wireless device 16 does notreceive an EPDCCH message, then the wireless device 16 is allowed toassume that aperiodic CSI-RS can be transmitted in the subframe in allthe REs belonging to the EPDCCH sets configured to the WD. It should benoted that these rules apply only when the wireless device 16 isconfigured to receive aperiodic CSI-RS which has no subframeconfiguration associated with it (i.e., the rules do not apply towireless devices not configured to receive aperiodic CSI-RStransmission). The steps related to this embodiment are illustrated inFIG. 20.

FIG. 20 is a flowchart of an exemplary process performed by a wirelessdevice 16 of avoiding collision between a downlink control channel and achannel state information reference signal. The process includesdetermining whether an EPDCCH message is received in an EPDCCH set in acurrent subframe, where the message that indicates an aperiodic CSI-RShas been transmitted (block S124). If so, the process includesdetermining whether an aperiodic CSI-RS is present in the currentsubframe (block S126). If so, the wireless device 16 assumes anaperiodic CSI-RS is not transmitted in any REs carrying an EPDCCHmessage in the current subframe (block S128). Returning to block S124,if the EPDCCH message is not received in an EPDCCH set in the currentsubframe indicating that an aperiodic CSI-RS has been transmitted, thena determination is made whether an aperiodic CSI-RS is present in thecurrent subframe (block S130). If so, the wireless device 16 assumes anaperiodic CSI-RS can be transmitted in all REs belonging to the EPDCCHsets in the current subframe (block S132).

In some variants, the network node 14 does not transmit aperiodic CSI-RSin any REs carrying an EPDCCH message to a wireless device if thewireless device receives an EPDCCH message that indicates an aperiodicCSI-RS has been transmitted in the subframe. If the presence ofaperiodic CSI-RS transmission in a subframe is indicated to the wirelessdevice 16 by the network node 14 via the PDCCH and the wireless device16 does not receive an EPDCCH message, then the network node 14 isallowed to transmit aperiodic CSI-RSs in the subframe in all the REsbelonging to the EPDCCH sets configured to the wireless device 16.

Embodiment 4

In the solutions discussed above, for a wireless device 16 configuredwith EPDCCH but not configured with aperiodic CSI-RS, its EPDCCHperformance can be degraded if the EPDCCH collides with aperiodic CSI-RStransmitted to other wireless devices 16.

In another embodiment, the network node 14 does not transmit aperiodicCSI-RS to any wireless device in PRBs configured for EPDCCH. The EPDCCHPRBs can be configured such that there is minimum impact on CSIestimation by not transmitting aperiodic CSI-RS in the PRBs. Forexample, the same EPDCCH PRBs may be configured for all wireless devicesand the PRBs may be equally spaced such as PRBs with indices {n, n+2,n+4, . . . }, where n is a non-negative integer. A wireless deviceconfigured with both EPDCCH and aperiodic CSI-RS may assume aperiodicCSI-RS is not transmitted on all PRBs configured for EPDCCH.

An example is shown in FIG. 21.

Three alternatives on how to capture the previous embodiments inspecification text is given.

The wireless device 16 shall assume that CSI reference signals are nottransmitted

-   -   in the downlink pilot time slot(s) (DwPTS) in case of frame        structure type 2,    -   in subframes where transmission of a CSI-RS would collide with        SystemInformationBlockType1 messages,    -   in the primary cell in subframes configured for transmission of        paging messages in the primary cell for any wireless device with        the cell-specific paging configuration,    -   Alt.1 . . . in physical resource-block pair(s) belonging to an        EPDCCH set configured to the wireless device in that subframe.    -   Alt.2 . . . in any physical resource-block pair(s) carrying an        EPDCCH associated with a trigger of the CSI reference signals        using an aperiodic trigger    -   Alt.3 . . . in any resource elements carrying an EPDCCH        associated with a trigger of the CSI reference signals using an        aperiodic trigger

FIG. 22 is a flowchart of an exemplary process in a network node 14 foravoiding collisions between a downlink control channel and an aperiodicchannel state information reference signal. The process includessignalling a wireless device 16 to configure, via the downlink controlchannel set configuration unit 52, the wireless device with a downlinkcontrol channel set that does not contain an aperiodic CSI-RS (blocks134). The process also includes signalling to the wireless device, viathe transmitter 32, an aperiodic CSI-RS, the presence of the CSI-RSbeing in a subframe in a downlink channel so as to enable the wirelessdevice 16 to assume that the CSI-RS is not present in physical layerresources contained within the downlink control channel set (blockS136).

FIG. 23 is a flowchart of an exemplary process in a wireless device 16for avoiding collisions between a downlink control channel and anaperiodic channel state information reference signal. The process mayinclude, optionally, receiving, via the receiver 20, signalling from anetwork node 14 to configure the wireless device 16 with a downlinkcontrol channel set (block S138). The process may also include,optionally, configuring the wireless device 16, via the downlink controlchannel set configuration unit 52, with the downlink control channel set(not shown)). The process may also include, optionally, receiving, viathe receiver 20, from the network node 14 on a physical control channelan indication of a presence of the aperiodic CSI-RS (block S142). Theprocess further may further include receiving, via the receiver 54, theaperiodic CSI-RS based on the assumption that the aperiodic CSI-RS isnot present in physical layer resources corresponding to the downlinkcontrol channel set not shown).

FIG. 24 is a flowchart of an exemplary process that includes receivingan aperiodic CSI-RS based on an assumption that the aperiodic CSI-RS isnot present in physical layer resources corresponding to a DL controlchannel set (block S146).

Thus, in some embodiments, a method in a wireless device 16 is provided.The method includes receiving an aperiodic channel state informationreference signal, aperiodic CSI-RS, based on an assumption that theaperiodic CSI-RS is not present in physical layer resourcescorresponding to a downlink control channel set. In some embodiments,the aperiodic CSI-RS can be transmitted in the physical layer resourcesin at least some defined conditions. In some embodiments, the methodincludes at least one of: receiving signalling to configure the wirelessdevice 16 for a downlink control channel set and receiving on a physicalcontrol channel an indication of a presence of the aperiodic CSI-RS. Insome embodiments, the indication of a presence of the aperiodic CSI-RSindicates that the aperiodic CSI-RS is present in one of a subframe or aslot. In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in a predeterminednumber of OFDM symbols.

In some embodiments, a method in a wireless device 16 is provided. Themethod includes receiving an aperiodic CSI-RS based on the assumptionthat the aperiodic CSI-RS is not present in physical layer resourcescontained within the downlink control channel set (block S144). Themethod may also include at least one of receiving signalling, e.g. froma network node 14 to configure the wireless device 16 with a downlinkcontrol channel set (block S138). The method may also includesconfiguring the wireless device 16 with the downlink control channel set(block S140). The method may also include receiving from the networknode 14 on a physical control channel an indication of a presence of theaperiodic CSI-RS (block S142).

In some embodiments, the wireless device 16 assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks(PRBs) belonging to the downlink control channel set with which thewireless device 16 is configured if the wireless device 16 receives adownlink control channel message in the subframe that indicates that anaperiodic CSI-RS has been transmitted in the downlink control channelset. In some embodiments, if a presence of the aperiodic CSI-RS in asubframe is indicated by a physical downlink control channel (PDCCH) andthe wireless device 16 does not receive a downlink control channelmessage in the downlink control channel set, then the wireless device 16assumes that aperiodic aperiodic CSI-RS is transmitted in the subframein the physical resource blocks (PRBs) belonging to the downlink controlchannel set. In some embodiments, a presence of the aperiodic CSI-RS ina subframe is indicated to the wireless device 16 via a physicaldownlink control channel (PDCCH) and if the wireless device 16 does notreceive a downlink control channel message that indicates that theaperiodic CSI-RS has been transmitted in the downlink control channelset, then the wireless device 16 assumes that the aperiodic CSI-RS iscontained in the physical resource blocks (PRBs) belonging to thedownlink control channel set in the subframe. In some embodiments, thewireless device 16 assumes that the aperiodic CSI-RS is not transmittedin a subframe in the physical resource blocks (PRBs) belonging to thedownlink control channel set with which the wireless device 16 isconfigured regardless of whether a downlink control channel message isreceived in the downlink control channel set.

In some embodiments, the wireless device 16 assumes that the aperiodicCSI-RS is not transmitted in a subframe of physical resource blocks(PRBs) carrying a downlink control channel message to the wirelessdevice 16 if the wireless device 16 receives a downlink control messagein the subframe that indicates that the aperiodic CSI-RS has beentransmitted. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated by a physical downlink control channel(PDCCH) and the wireless device 16 does not receive a downlink controlchannel message, then the wireless device 16 assumes the aperiodicCSI-RS is transmitted in the subframe in the physical resource blocks(PRBs) belonging to the downlink control channel set with which thewireless device 16 is configured. In some embodiments, the wirelessdevice 16 assumes that a network node 14 does not transmit aperiodicCSI-RS in the physical resource blocks, PRBs, carrying a downlinkcontrol channel message to that wireless device 16 if the wirelessdevice 16 receives a downlink control channel message that indicatesthat an aperiodic CSI-RS has been transmitted in the subframe. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated to the wireless device 16 via a physical downlink controlchannel (PDCCH) and if the wireless device 16 does not receive adownlink control channel message, then the wireless device 16 assumesthat aperiodic CSI-RS is transmitted to the wireless device 16 in thephysical resource blocks (PRBs) belonging to the downlink controlchannel set with which the wireless device 16 is configured in thesubframe.

In some embodiments, the wireless device 16 assumes that the aperiodicCSI-RS is not transmitted in a subframe in any resource elements, REs,carrying a downlink control channel message to the wireless device 16 ifthe wireless device 16 receives a downlink control channel message inthe subframe. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated by a physical downlink control channel(PDCCH) and the wireless device 16 does not receive a downlink controlchannel message, then the wireless device 16 assumes that the aperiodicCSI-RS can be transmitted in the subframe in all resource elements, REs,belonging to the downlink control channel set with which the wirelessdevice 16 is configured. In some embodiments, the wireless device 16assumes that aperiodic CSI-RS are not transmitted in a downlink pilottime slot in a case of frame structure type 2. In some embodiments, thewireless device 16 assumes that aperiodic CSI-RS are not transmitted insubframes where transmission of the aperiodic CSI-RS would collide witha SystemInformationBlockType1 message. In some embodiments, the wirelessdevice 16 assumes that aperiodic CSI-RS are not transmitted in physicalresource block pairs belonging to the downlink control channel set withwhich the wireless device 16 is configured in the subframe.

In some embodiments, the wireless device 16 assumes that aperiodicCSI-RS are not transmitted in physical resource block pairs carrying thedownlink control channel associated with a trigger of the aperiodicCSI-RS using an aperiodic trigger. In some embodiments, the wirelessdevice 16 assumes that aperiodic CSI-RS are not transmitted in anyresource elements (RE) carrying the downlink control channel associatedwith a trigger of the aperiodic CSI-RS using an aperiodic trigger. Insome embodiments, the downlink control channel is an enhanced physicaldownlink control channel (EPDCCH) and a downlink control channel messageis an EPDCCH message in a long term evolution communication system. Insome embodiments, the downlink control channel set is a core set in aNew Radio, NR, communication system.

In some embodiments, a wireless device 16 configured to avoid collisionbetween a downlink control channel and a channel state informationreference signal (aperiodic CSI-RS) is provided. The wireless device 16includes processing circuitry 42 configured to: configure the wirelessdevice 16 with a downlink control channel set according to signallingreceived from a network node. The wireless device 16 further includes atransceiver 48 configured to receive signalling from a network node 14to configure the wireless device 16 with the downlink control channelset. The transceiver 48 is further configured to receive from thenetwork node 14 on a physical control channel an indication of apresence of the aperiodic CSI-RS in a subframe. The transceiver 48 isfurther configured to receive the aperiodic CSI-RS based on theassumption that the aperiodic CSI-RS is not present in physical layerresources contained within the downlink control channel set. In someembodiments, the indication of a presence of the aperiodic CSI-RSindicates that the aperiodic CSI-RS is present in one of a subframe or aslot. In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in a predeterminednumber of OFDM symbols.

In some embodiments, the wireless device 16 assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks(PRBs) belonging to the downlink control channel set with which thewireless device 16 is configured if the wireless device 16 receives adownlink control channel message in the subframe that indicates that anaperiodic CSI-RS has been transmitted in the downlink control channelset. In some embodiments, if a presence of the aperiodic CSI-RS in asubframe is indicated by a physical downlink control channel (PDCCH) andthe wireless device 16 does not receive a downlink control channelmessage in the downlink control channel set, then the wireless device 16assumes that aperiodic aperiodic CSI-RS is transmitted in the subframein the physical resource blocks (PRBs) belonging to the downlink controlchannel set. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device 16 via a physicaldownlink control channel (PDCCH) and if the wireless device 16 does notreceive a downlink control channel message that indicates that theaperiodic CSI-RS has been transmitted in the downlink control channelset, then the wireless device 16 assumes that the aperiodic CSI-RS iscontained in the physical resource blocks (PRBs) belonging to thedownlink control channel set in the subframe.

In some embodiments, the wireless device 16 assumes that aperiodicaperiodic CSI-RS is not transmitted in a subframe in the physicalresource blocks (PRBs) belonging to the downlink control channel setwith which the wireless device 16 is configured regardless of whether adownlink control channel message is received in the downlink controlchannel set. In some embodiments, the wireless device 16 assumes thatthe aperiodic CSI-RS is not transmitted in a subframe of physicalresource blocks (PRBs) carrying a downlink control channel message tothe wireless device 16 if the wireless device 16 receives a downlinkcontrol message in the subframe that indicates that the aperiodic CSI-RShas been transmitted. In some embodiments, if a presence of theaperiodic CSI-RS in a subframe is indicated by a physical downlinkcontrol channel (PDCCH) and the wireless device 16 does not receive adownlink control channel message, then the wireless device 16 assumesthe aperiodic CSI-RS is transmitted in the subframe in the physicalresource blocks (PRBs) belonging to the downlink control channel setwith which the wireless device 16 is configured.

In some embodiments, the wireless device 16 assumes that a network node14 does not transmit aperiodic CSI-RS in the physical resource blocks(PRBs) carrying a downlink control channel message to that wirelessdevice 16 if the wireless device 16 receives a downlink control channelmessage that indicates that an aperiodic CSI-RS has been transmitted inthe subframe. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device 16 via a physicaldownlink control channel (PDCCH) and if the wireless device 16 does notreceive a downlink control channel message, then the wireless device 16assumes that aperiodic CSI-RS is transmitted to the wireless device 16in the physical resource blocks (PRBs) belonging to the downlink controlchannel set with which the wireless device 16 is configured in thesubframe. In some embodiments, the wireless device 16 assumes that theaperiodic CSI-RS is not transmitted in a subframe in any resourceelements, REs, carrying a downlink control channel message to thewireless device 16 if the wireless device 16 receives a downlink controlchannel message in the subframe. In some embodiments, if a presence ofthe aperiodic CSI-RS in a subframe is indicated by a physical downlinkcontrol channel (PDCCH) and the wireless device 16 does not receive adownlink control channel message, then the wireless device 16 assumesthat the aperiodic CSI-RS can be transmitted in the subframe in allresource elements, REs, belonging to the downlink control channel setwith which the wireless device 16 is configured.

In some embodiments, the wireless device 16 assumes that aperiodicCSI-RS are not transmitted in a downlink pilot time slot in a case offrame structure type 2. In some embodiments, the wireless device 16assumes that aperiodic CSI-RS are not transmitted in subframes wheretransmission of the aperiodic CSI-RS would collide with aSystemInformationBlockType1 message. In some embodiments, the wirelessdevice 16 assumes that aperiodic CSI-RS are not transmitted in physicalresource block pairs belonging to the downlink control channel set withwhich the wireless device 16 is configured in the subframe. In someembodiments, the wireless device 16 assumes that aperiodic CSI-RS arenot transmitted in physical resource block pairs carrying the downlinkcontrol channel associated with a trigger of the aperiodic CSI-RS usingan aperiodic trigger. In some embodiments, the wireless device 16assumes that aperiodic CSI-RS are not transmitted in any resourceelements, RE, carrying the downlink control channel associated with atrigger of the aperiodic CSI-RS using an aperiodic trigger. In someembodiments, the downlink control channel is an enhanced physicaldownlink control channel (EPDCCH), and a downlink control channelmessage is an EPDCCH message in a long term evolution communicationsystem. In some embodiments, the downlink control channel set is a coreset in a New Radio, NR, communication system.

In some embodiments, a wireless device 16 configured to avoid collisionbetween downlink control channel and a channel state informationreference signal (aperiodic CSI-RS), is provided. The wireless device 16includes a downlink control channel set configuration receiver module 20configured to receive signalling from a network node 14 to configure thewireless device 16 with a downlink control channel set. The wirelessdevice 16 also includes a downlink control channel set configurationmodule 53 configured to configure the wireless device 16 with a downlinkcontrol channel set according to signalling received from a network node14. The wireless device 16 further includes an aperiodic CSI-RSindication receiver module 55 configured to receive from the networknode on a physical control channel an indication of a presence of theaperiodic CSI-RS in a subframe. The wireless device 16 also includes anaperiodic CSI-RS receiver module 57 configured to receive the aperiodicCSI-RS based on the assumption that the aperiodic CSI-RS is not presentin physical layer resources contained within the downlink controlchannel set.

In some embodiments, a method in a network node 14 of avoiding collisionbetween a downlink control channel and a channel state informationreference signal, aperiodic CSI-RS, is provided. The method includessignalling a wireless device 16 to configure the wireless device 16 witha downlink control channel set that does not contain an aperiodic CSI-RS(block S134). The method also includes signalling to the wireless device16 an aperiodic CSI-RS, the presence of the aperiodic CSI-RS being in asubframe in a downlink channel so as to enable the wireless device 16 toassume that the aperiodic CSI-RS is not present in physical layerresources contained within the downlink control channel set (blockS136).

In some embodiments, the network node does not transmit the aperiodicCSI-RS to the wireless device in a subframe in the physical resourceblocks(PRBs) belonging to the downlink control channel set configured tothe wireless device. In some embodiments, the network node indicates apresence of the aperiodic CSI-RS in the subframe and the wireless devicedoes not assume that the aperiodic CSI-RS is not present in the downlinkcontrol channel set. In some embodiments, the network node 14 indicatesa presence of the aperiodic CSI-RS in the subframe and transmits theaperiodic CSI-RS in the subframe in all resource elements belonging tothe downlink control channel set.

In some embodiments, a network node 14 configured for avoiding collisionbetween a downlink control channel and a channel state informationreference signal, aperiodic CSI-RS is provided. The network node 14includes a transceiver 28 configured to signal to a wireless device 16to configure the wireless device 16 with a downlink control channel setthat does not contain an aperiodic CSI-RS. The transceiver 28 isconfigured to signal to the wireless device an aperiodic CSI-RS, thepresence of the aperiodic CSI-RS being in a subframe in a downlinkchannel so as to enable the wireless device 16 to assume that theaperiodic CSI-RS is not present in physical layer resources containedwithin the downlink control channel set.

In some embodiments, the network node 14 does not transmit the aperiodicCSI-RS to the wireless device 16 in a subframe in the physical resourceblocks(PRBs) belonging to the downlink control channel set configured tothe wireless device 16. In some embodiments, the network node 14indicates a presence of the aperiodic CSI-RS in the subframe and thewireless device 16 does not assume that the aperiodic CSI-RS is notpresent in the downlink control channel set. In some embodiments, thenetwork node 16 indicates a presence of the aperiodic CSI-RS in thesubframe and transmits the aperiodic CSI-RS in the subframe in allresource elements belonging to the downlink control channel set.

In some embodiments, a network node 14 configured for avoiding collisionbetween a downlink control channel and a channel state informationreference signal, aperiodic CSI-RS, is provided. The network node 14includes a transceiver module 29 configured to signal to a wirelessdevice 16 to configure the wireless device 16 with a downlink controlchannel set that does not contain an aperiodic CSI-RS. The transceivermodule 29 is also configured to signal to the wireless device 16 anaperiodic CSI-RS, the presence of the aperiodic CSI-RS being in asubframe in a downlink channel so as to enable the wireless device 16 toassume that the aperiodic CSI-RS is not present in physical layerresources contained within (or corresponding to) the downlink controlchannel set.

In the present disclosure “resources belonging to” may be interpreted as“resources corresponding to”, as it will be recognized by a personskilled in the art.

Some embodiments include the following.Embodiment 1. A method of avoiding collision between an EPDCCH and aCSI-RS in a wireless device, the method comprising receiving signalingthat configures the wireless device with EPDCCH set(s) and to receivethe CSI-RS, wherein the presence of the CSI-RS in a subframe isindicated to the wireless device in a physical control channel; andreceiving the CSI-RS based on the assumption that the CSI-RS is notpresent in physical layer resources contained within the EPDCCH set(s).Embodiment 2. The method of Embodiment 1, wherein the wireless devicecan assume that the CSI-RS is not transmitted in a subframe in the PRBsbelonging to an EPDCCH set configured to the WD.Embodiment 3. The method of Embodiment 1, wherein the wireless devicecan assume that the CSI-RS is not transmitted in the PRBs belonging toan EPDCCH set in a subframe if the wireless device receives an EPDCCHmessage that indicates the CSI-RS has been transmitted in that EPDCCHset in the subframe.Embodiment 4. The method of Embodiment 1, wherein the wireless device isallowed to assume that the CSI-RS is transmitted in the PRBs belongingto that EPDCCH set in a subframe if the presence of the CSI-RStransmission in a subframe is indicated by PDCCH and the wireless devicedoes not receive an EPDCCH message in an EPDCCH set.Embodiment 5. The method of Embodiment 1, wherein the wireless devicecan assume that the CSI-RS is not transmitted in a subframe in the PRBscarrying an EPDCCH message that indicates the CSI-RS has beentransmitted to the wireless device if the wireless device receives anEPDCCH message in the subframe.Embodiment 6. The method of Embodiment 1, wherein the wireless devicecan assume that the CSI-RS is not transmitted in a subframe in any REscarrying an EPDCCH message to the wireless device if the wireless devicereceives an EPDCCH message that indicates the CSI-RS has beentransmitted in the subframe.Embodiment 7. A wireless device configured to avoid collision betweenand EPDCCH and a CSI-RS, the wireless device comprising:

processing circuitry including a memory and a processor, the memorycontaining instructions that when executed by the processor, cause theprocessor to:

receive signalling that configures the wireless device with EPDCCHset(s) and to receive the CSI-RS, wherein the presence of the CSI-RS ina subframe is indicated to the wireless device in a physical controlchannel; and

receive the CSI-RS based on the assumption that the CSI-RS is notpresent in physical layer resources contained within the EPDCCH set(s).

Embodiment 8. The wireless device of Embodiment 7, wherein the wirelessdevice can assume that the CSI-RS is not transmitted in a subframe inthe PRBs belonging to an EPDCCH set configured to the WD.Embodiment 9. The wireless device of Embodiment 7, wherein the wirelessdevice can assume that the CSI-RS is not transmitted in the PRBsbelonging to an EPDCCH set in a subframe if the wireless device receivesan EPDCCH message that indicates the CSI-RS has been transmitted in thatEPDCCH set in the subframe.Embodiment 10. The wireless device of Embodiment 7, wherein the wirelessdevice is allowed to assume that the CSI-RS is transmitted in the PRBsbelonging to that EPDCCH set in a subframe if the presence of the CSI-RStransmission in a subframe is indicated by PDCCH and the wireless devicedoes not receive an EPDCCH message in an EPDCCH set.Embodiment 11. The wireless device of Embodiment 7, wherein the wirelessdevice can assume that the CSI-RS is not transmitted in a subframe inthe PRBs carrying an EPDCCH message that indicates the CSI-RS has beentransmitted to the wireless device if the wireless device receives anEPDCCH message in the subframe.Embodiment 12. The wireless device of Embodiment 7, wherein the wirelessdevice can assume that the CSI-RS is not transmitted in a subframe inany REs carrying an EPDCCH message to the wireless device if thewireless device receives an EPDCCH message that indicates the CSI-RS hasbeen transmitted in the subframe.Embodiment 13. A wireless device configured to avoid collision betweenan EPDCCH and a CSI-RS, the wireless device comprising:

an EPDCCH configuration module configured to receive signalling thatconfigures the wireless device with EPDCCH set(s) and to receive theCSI-RS, wherein the presence of the CSI-RS in a subframe is indicated tothe wireless device in a physical control channel; and

a CSI-RS receiver module configured to receive the CSI-RS based on theassumption that the CSI-RS is not present in physical layer resourcescontained within the EPDCCH set(s).

In some embodiments, a method in a wireless device is provided. Themethod includes receiving the aperiodic CSI-RS based on the assumptionthat the aperiodic CSI-RS is not present in physical layer resourcescontained within the downlink control channel set. The method may alsoinclude receiving signalling to configure the wireless device with adownlink control channel set. The method may also include receiving fromthe network node on a physical control channel an indication of apresence of the aperiodic CSI-RS in a subframe.

In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in one of asubframe or a slot. In some embodiments, the indication of a presence ofthe aperiodic CSI-RS indicates that the aperiodic CSI-RS is present in apredetermined number of OFDM symbols.

In some embodiments, the aperiodic CSI-RS can be transmitted in thephysical layer resources in at least some defined conditions.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks,PRBs, corresponding to the downlink control channel set with which thewireless device is configured if the wireless device receives a downlinkcontrol channel message in the subframe that indicates that an aperiodicCSI-RS has been transmitted in the downlink control channel set. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message in thedownlink control channel set, then the wireless device assumes thataperiodic CSI-RS is transmitted in the subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel set. In someembodiments, a presence of the aperiodic CSI-RS in a subframe isindicated to the wireless device via a downlink control channel, such asPDCCH, and if the wireless device does not receive a downlink controlchannel message that indicates that the aperiodic CSI-RS has beentransmitted in the downlink control channel set, then the wirelessdevice assumes that the aperiodic CSI-RS is contained in the physicalresource blocks, PRBs, corresponding to the downlink control channel setin the subframe. In some embodiments, the wireless device assumes thatthe aperiodic CSI-RS is not transmitted in a subframe in the physicalresource blocks, PRBs, corresponding to the downlink control channel setwith which the wireless device is configured regardless of whether adownlink control channel message is received in the downlink controlchannel set.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe of physical resource blocks,PRBs, carrying a downlink control channel message to the wireless deviceif the wireless device receives a downlink control message in thesubframe that indicates that the aperiodic CSI-RS has been transmitted.In some embodiments, if a presence of the aperiodic CSI-RS in a subframeis indicated by a downlink control channel, such as PDCCH, and thewireless device does not receive a downlink control channel message,then the wireless device assumes the aperiodic CSI-RS is transmitted inthe subframe in the physical resource blocks, PRBs, corresponding to thedownlink control channel set with which the wireless device isconfigured. In some embodiments, the wireless device assumes that anetwork node does not transmit aperiodic CSI-RS in the physical resourceblocks, PRBs, carrying a downlink control channel message to thatwireless device if the wireless device receives a downlink controlchannel message that indicates that a aperiodic CSI-RS has beentransmitted in the subframe. In some embodiments, if a presence of theaperiodic CSI-RS in a subframe is indicated to the wireless device via adownlink control channel, such as PDCCH, and if the wireless device doesnot receive a downlink control channel message, then the wireless deviceassumes that aperiodic CSI-RS is transmitted to the wireless device inthe physical resource blocks, PRBs, corresponding to the downlinkcontrol channel set with which the wireless device is configured in thesubframe.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in any resource elements, REs,carrying a downlink control channel message to the wireless device ifthe wireless device receives a downlink control channel message in thesubframe. In some embodiments, if a presence of the aperiodic CSI-RS ina subframe is indicated by a downlink control channel, such as PDCCH,and the wireless device does not receive a downlink control channelmessage, then the wireless device assumes that the aperiodic CSI-RS canbe transmitted in the subframe in all resource elements, REs,corresponding to the downlink control channel set with which thewireless device is configured. In some embodiments, the wireless deviceassumes that aperiodic CSI-RS are not transmitted in a downlink pilottime slot in a case of frame structure type 2. In some embodiments, thewireless device assumes that aperiodic CSI-RS are not transmitted insubframes where transmission of the aperiodic CSI-RS would collide witha SystemInformationBlockType1 message. In some embodiments, the wirelessdevice assumes that aperiodic CSI-RS are not transmitted in physicalresource block pairs corresponding to the downlink control channel setwith which the wireless device is configured in the subframe.

In some embodiments, the wireless device assumes that aperiodic CSI-RSare not transmitted in physical resource block pairs carrying thedownlink control channel associated with a trigger of the aperiodicCSI-RS using an aperiodic trigger. In some embodiments, the wirelessdevice assumes that aperiodic CSI-RS are not transmitted in any resourceelements, RE, carrying the downlink control channel associated with atrigger of the aperiodic CSI-RS using an aperiodic trigger. In someembodiments, the downlink control channel is an enhanced physicaldownlink control channel, EPDCCH, and a downlink control channel messageis an EPDCCH message in a long term evolution communication system.

In some embodiments, a wireless device is provided. The wireless deviceincludes processing circuitry configured to receive the aperiodic CSI-RSbased on the assumption that the aperiodic CSI-RS is not present inphysical layer resources contained within the downlink control channelset. The processing circuitry may be further configured to receivesignalling from a network node to configure the wireless device with thedownlink control channel set and/or to receive from the network node ona physical control channel an indication of a presence of the aperiodicCSI-RS.

In some embodiments, the wireless device assumes that the aperiodicCSI-RS is not transmitted in a subframe in physical resource blocks,PRBs, corresponding to the downlink control channel set with which thewireless device is configured if the wireless device receives a downlinkcontrol channel message in the subframe that indicates that an aperiodicCSI-RS has been transmitted in the downlink control channel set. In someembodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message in thedownlink control channel set, then the wireless device assumes thataperiodic aperiodic CSI-RS is transmitted in the subframe in thephysical resource blocks, PRBs, corresponding to the downlink controlchannel set. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device via a downlink controlchannel, such as PDCCH, and if the wireless device does not receive adownlink control channel message that indicates that the aperiodicCSI-RS has been transmitted in the downlink control channel set, thenthe wireless device assumes that the aperiodic CSI-RS is contained inthe physical resource blocks, PRBs, corresponding to the downlinkcontrol channel set in the subframe.

In some embodiments, the wireless device assumes that aperiodicaperiodic CSI-RS is not transmitted in a subframe in the physicalresource blocks, PRBs, corresponding to the downlink control channel setwith which the wireless device is configured regardless of whether adownlink control channel message is received in the downlink controlchannel set. In some embodiments, the wireless device assumes that theaperiodic CSI-RS is not transmitted in a subframe of physical resourceblocks, PRBs, carrying a downlink control channel message to thewireless device if the wireless device receives a downlink controlmessage in the subframe that indicates that the aperiodic CSI-RS hasbeen transmitted. In some embodiments, if a presence of the aperiodicCSI-RS in a subframe is indicated by a downlink control channel, such asPDCCH, and the wireless device does not receive a downlink controlchannel message, then the wireless device assumes the aperiodic CSI-RSis transmitted in the subframe in the physical resource blocks, PRBs,corresponding to the downlink control channel set with which thewireless device is configured.

In some embodiments, the wireless device assumes that a network nodedoes not transmit aperiodic CSI-RS in the physical resource blocks,PRBs, carrying a downlink control channel message to that wirelessdevice if the wireless device receives a downlink control channelmessage that indicates that a aperiodic CSI-RS has been transmitted inthe subframe. In some embodiments, if a presence of the aperiodic CSI-RSin a subframe is indicated to the wireless device via a downlink controlchannel, such as PDCCH, and if the wireless device does not receive adownlink control channel message, then the wireless device assumes thataperiodic CSI-RS is transmitted to the wireless device in the physicalresource blocks, PRBs, corresponding to the downlink control channel setwith which the wireless device is configured in the subframe. In someembodiments, the wireless device assumes that the aperiodic CSI-RS isnot transmitted in a subframe in any resource elements, REs, carrying adownlink control channel message to the wireless device if the wirelessdevice receives a downlink control channel message in the subframe. Insome embodiments, if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the wirelessdevice does not receive a downlink control channel message, then thewireless device assumes that the aperiodic CSI-RS can be transmitted inthe subframe in all resource elements, REs, corresponding to thedownlink control channel set with which the wireless device isconfigured.

In some embodiments, the wireless device assumes that aperiodic CSI-RSare not transmitted in a downlink pilot time slot in a case of framestructure type 2. In some embodiments, the wireless device assumes thataperiodic CSI-RS are not transmitted in subframes where transmission ofthe aperiodic CSI-RS would collide with a SystemInformationBlockType1message. In some embodiments, the wireless device assumes that aperiodicCSI-RS are not transmitted in physical resource block pairscorresponding to the downlink control channel set with which thewireless device is configured in the subframe. In some embodiments, thewireless device assumes that aperiodic CSI-RS are not transmitted inphysical resource block pairs carrying the downlink control channelassociated with a trigger of the aperiodic CSI-RS using an aperiodictrigger. In some embodiments, the wireless device assumes that aperiodicCSI-RS are not transmitted in any resource elements, RE, carrying thedownlink control channel associated with a trigger of the aperiodicCSI-RS using an aperiodic trigger. In some embodiments, the downlinkcontrol channel is an enhanced physical downlink control channel,EPDCCH, and a downlink control channel message is an EPDCCH message in along term evolution communication system.

In some embodiments, a wireless device configured to avoid collisionbetween downlink control channel and a channel state informationreference signal, aperiodic CSI-RS, is provided. The wireless deviceincludes a downlink control channel set configuration receiver moduleconfigured to receive signalling from a network node to configure thewireless device with a downlink control channel set. The wireless devicealso includes a downlink control channel set configuration moduleconfigured to configure the wireless device with a downlink controlchannel set according to signalling received from a network node. Thewireless device further includes a aperiodic CSI-RS indication receivermodule configured to receive from the network node on a physical controlchannel an indication of a presence of the aperiodic CSI-RS in asubframe. The wireless device also includes a aperiodic CSI-RS receivermodule configured to receive the aperiodic CSI-RS based on theassumption that the aperiodic CSI-RS is not present in physical layerresources contained within the downlink control channel set.

In some embodiments, a method in a network node is provided. The methodincludes signalling a wireless device to configure the wireless devicewith a downlink control channel set that does not contain a aperiodicCSI-RS. The method also includes signalling to the wireless device aaperiodic CSI-RS, the presence of the aperiodic CSI-RS in a downlinkchannel so as to enable the wireless device to assume that the aperiodicCSI-RS is not present in physical layer resources contained within thedownlink control channel set.

In some embodiments, the network node does not transmit the aperiodicCSI-RS to the wireless device in a subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel setconfigured to the wireless device. In some embodiments, the network nodeindicates a presence of the aperiodic CSI-RS in the subframe and thewireless device does not assume that the aperiodic CSI-RS is not presentin the downlink control channel set. In some embodiments, the networknode indicates a presence of the aperiodic CSI-RS in the subframe andtransmits the aperiodic CSI-RS in the subframe in all resource elementscorresponding to the downlink control channel set.

In some embodiments, a network node is provided. The network nodeincludes processing circuitry configured to signal to a wireless deviceto configure the wireless device with a downlink control channel setthat does not contain a aperiodic CSI-RS. The transceiver is configuredto signal to the wireless device a aperiodic CSI-RS, the presence of theaperiodic CSI-RS in a downlink channel so as to enable the wirelessdevice to assume that the aperiodic CSI-RS is not present in physicallayer resources contained within the downlink control channel set.

In some embodiments, the network node does not transmit the aperiodicCSI-RS to the wireless device in a subframe in the physical resourceblocks, PRBs, corresponding to the downlink control channel setconfigured to the wireless device. In some embodiments, the network nodeindicates a presence of the aperiodic CSI-RS in the subframe and thewireless device does not assume that the aperiodic CSI-RS is not presentin the downlink control channel set. In some embodiments, the networknode indicates a presence of the aperiodic CSI-RS in the subframe andtransmits the aperiodic CSI-RS in the subframe in all resource elementscorresponding to the downlink control channel set.

In some embodiments, a network node is provided. The network nodeincludes a transceiver module configured to signal to a wireless deviceto configure the wireless device with a downlink control channel setthat does not contain a aperiodic CSI-RS. The transceiver module is alsoconfigured to signal to the wireless device a aperiodic CSI-RS, thepresence of the aperiodic CSI-RS being in a subframe in a downlinkchannel so as to enable the wireless device to assume that the aperiodicCSI-RS is not present in physical layer resources contained within thedownlink control channel set.

In some embodiments, the indication of a presence of the aperiodicCSI-RS indicates that the aperiodic CSI-RS is present in one of asubframe or a slot. In some embodiments, the indication of a presence ofthe aperiodic CSI-RS indicates that the aperiodic CSI-RS is present in apredetermined number of OFDM symbols.

In some embodiments, the aperiodic CSI-RS can be transmitted in thephysical layer resources in at least some defined conditions.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,and/or computer program product. Accordingly, the concepts describedherein may take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.”Furthermore, the disclosure may take the form of a computer programproduct on a tangible computer usable storage medium having computerprogram code embodied in the medium that can be executed by a computer.Any suitable tangible computer readable medium may be utilized includinghard disks, CD-ROMs, electronic storage devices, optical storagedevices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings withoutdeparting from the scope of the following claims.

What is claimed is:
 1. A method in a user equipment (16), the methodcomprising: receiving an aperiodic channel state information referencesignal, aperiodic CSI-RS, based on an assumption that the aperiodicCSI-RS is not present in physical layer resources corresponding to adownlink control channel set (S146).
 2. The method of claim 1, whereinthe aperiodic CSI-RS can be transmitted in the physical layer resourcesin at least some defined conditions.
 3. The method of claim 1, furthercomprising at least one of: receiving signaling to configure the userequipment (16) for a downlink control channel set (S138); and receivingon a physical control channel an indication of a presence of theaperiodic CSI-RS (S142).
 4. The method of claim 3, wherein theindication of a presence of the aperiodic CSI-RS indicates that theaperiodic CSI-RS is present in a predetermined number of OFDM symbols.5. The method of claim 1, wherein the user equipment (16) assumes thatthe aperiodic CSI-RS is not transmitted in a subframe in physicalresource blocks, PRBs, belonging to the downlink control channel setwith which the user equipment (16) is configured if the user equipment(16) receives a downlink control channel message in the subframe thatindicates that an aperiodic CSI-RS has been transmitted in the downlinkcontrol channel set.
 6. The method of claim 1, wherein if a presence ofthe aperiodic CSI-RS in a subframe is indicated by a downlink controlchannel, such as PDCCH, and the user equipment (16) does not receive adownlink control channel message in the downlink control channel set,then the user equipment (16) assumes that aperiodic CSI-RS istransmitted in the subframe in physical resource blocks, PRBs, belongingto the downlink control channel set.
 7. The method of claim 1, whereinif a presence of the aperiodic CSI-RS in a subframe is indicated to theuser equipment (16) via a downlink control channel, such as PDCCH, andif the user equipment (16) does not receive a downlink control channelmessage that indicates that the aperiodic CSI-RS has been transmitted inthe downlink control channel set, then the user equipment (16) assumesthat the aperiodic CSI-RS is contained in the physical resource blocks,PRBs, belonging to the downlink control channel set in the subframe. 8.The method of claim 1, wherein the user equipment (16) assumes that theaperiodic CSI-RS is not transmitted in a subframe in the physicalresource blocks, PRBs, belonging to the downlink control channel setwith which the user equipment (16) is configured regardless of whether adownlink control channel message is received in the downlink controlchannel set.
 9. The method of claim 1, wherein the user equipment (16)assumes that the aperiodic CSI-RS is not transmitted in a subframe ofthe physical resource blocks, PRBs, carrying a downlink control channelmessage to the user equipment (16) if the user equipment (16) receives adownlink control message in the subframe that indicates that theaperiodic CSI-RS has been transmitted.
 10. The method of claim 1,wherein if a presence of the aperiodic CSI-RS in a subframe is indicatedby a downlink control channel, such as PDCCH, and the user equipment(16) does not receive a downlink control channel message, then the userequipment (16) assumes the aperiodic CSI-RS is transmitted in thesubframe in the physical resource blocks, PRBs, belonging to thedownlink control channel set with which the user equipment (16) isconfigured.
 11. The method of claim 1, wherein the user equipment (16)assumes that a base station (14) does not transmit aperiodic CSI-RS inthe physical resource blocks, PRBs, carrying a downlink control channelmessage to that user equipment (16) if the user equipment (16) receivesa downlink control channel message that indicates that an aperiodicCSI-RS has been transmitted in the subframe.
 12. The method of claim 1,wherein if a presence of the aperiodic CSI-RS in a subframe is indicatedto the user equipment (16) via a downlink control channel, such asPDCCH, and if the user equipment (16) does not receive a downlinkcontrol channel message, then the user equipment (16) assumes thataperiodic CSI-RS is transmitted to the user equipment (16) in thephysical resource blocks, PRBs, belonging to the downlink controlchannel set with which the user equipment (16) is configured in thesubframe.
 13. The method of claim 1, wherein the user equipment (16)assumes that the aperiodic CSI-RS is not transmitted in a subframe inany resource elements, REs, carrying a downlink control channel messageto the user equipment (16) if the user equipment (16) receives adownlink control channel message in the subframe.
 14. The method ofclaim 1, wherein if a presence of the aperiodic CSI-RS in a subframe isindicated by a downlink control channel, such as PDCCH, and the userequipment (16) does not receive a downlink control channel message, thenthe user equipment (16) assumes that the aperiodic CSI-RS can betransmitted in the subframe in all resource elements, REs, belonging tothe downlink control channel set with which the user equipment (16) isconfigured.
 15. The method of claim 1, wherein the user equipment (16)assumes that the aperiodic CSI-RS is not transmitted in a downlink pilottime slot, DwPTS, for frame structure type
 2. 16. A user equipment (16)comprising: processing circuitry (42) configured to: receive theaperiodic CSI-RS based on an assumption that the aperiodic CSI-RS is notpresent in physical layer resource corresponding to the downlink controlchannel set; receive signalling to configure the user equipment (16)with the downlink control channel set; and receive on a physical controlchannel an indication of a presence of the aperiodic CSI-RS.
 17. Theuser equipment (16) of claim 16, wherein the indication of a presence ofthe aperiodic CSI-RS indicates that the aperiodic CSI-RS is present inone of a subframe or a slot.
 18. The user equipment (16) of claim 16,wherein the indication of a presence of the aperiodic CSI-RS indicatesthat the aperiodic CSI-RS is present in a predetermined number of OFDMsymbols.
 19. A method in a base station (14), the method comprising:signalling a user equipment (16) to configure the user equipment (16)with a downlink control channel set that does not contain an aperiodicCSI-RS (S134); and signalling to the user equipment (16) an aperiodicCSI-RS, a presence of the aperiodic CSI-RS in a downlink channel toenable the user equipment (16) to assume that the aperiodic CSI-RS isnot present in physical layer resources corresponding to the downlinkcontrol channel set (S136), the base station (14) not transmitting theaperiodic CSI-RS to the user equipment (16) in a subframe in thephysical resource blocks, PRBs, corresponding to the downlink controlchannel set configured to the user equipment (16).
 20. The method ofclaim 19, wherein the base station (14) indicates a presence of theaperiodic CSI-RS in a subframe and the user equipment (16) does notassume that the aperiodic CSI-RS is not present in the downlink controlchannel set.